Prenatal Testing: Ultrasound Safety and Accuracy

by Kmom

Copyright © 1996-2003 Kmom@Vireday.Com. All rights reserved.

Last updated:  March 2003

DISCLAIMER: The information on this website is not intended and should not be construed as medical advice. Consult your health provider.

SPECIAL NOTE: It is not in the scope of this FAQ to truly cover prenatal testing thoroughly, only to address it in general and as it concerns big moms. Kmom urges all pregnant women to thoroughly research any test before deciding whether to use it or not. Do NOT accept blindly what your doctor tells you. Ask questions and consider all sides of the issue. Testing decisions vary greatly depending on family history, medical condition, parental beliefs, etc. For more information on prenatal testing, see the FAQs available from on the Internet.

The following FAQ contains general information about ultrasounds, how they are done, types of ultrasounds available, the technology used in ultrasounds, the safety and accuracy of ultrasounds, and the justification (or lack thereof) for various indications for ultrasounds.  

For more information about ultrasounds in women of size, please see the FAQ on Ultrasounds in Women of Size.  Big moms should read THIS FAQ first before reading the other FAQ so that they can understand the full implications of ultrasounds in general, before reading how they impact big moms in particular.  



"The technology of prenatal diagnosis is usually presented to us as a solution, but it brings with it problems of its own...the technology of prenatal diagnosis has changed and continues to change women's experience of pregnancy."  

---Barbara Katz Rothman, The Tentative Pregnancy


Note: The introduction is the same in each section of the Prenatal Testing FAQs. If you've already read it, you may want to skip ahead.  

All pregnant women in our technology-happy modern society face confusing choices about prenatal testing, its advantages and disadvantages, and its appropriateness for them. Large pregnant women face even more confusion, since prenatal testing can be slightly harder in this population, and the results can be more confusing. However, since they may be at a somewhat increased risk for problems like neural tube defects, they also face greater pressure than others to have these prenatal tests, even though the tests are often difficult to interpret.

This section is an attempt to present an overview of the most basic prenatal tests most pregnant women in the US are pressured to have, including Ultrasounds, the AFP/Triple Screen Test, Gestational Diabetes tests, and under certain conditions, Amniocentesis.  It is further designed to address the special concerns that large women might have in taking these tests---their fears, any special equipment or techniques that might be helpful, the controversies over interpretation of results, whether large women have a higher rate of so-called 'false-positives' on certain tests and why, etc.

It's important to remember that discussing prenatal tests can be simple or incredibly complicated, depending on the degree of detail that is needed and the point under discussion. This FAQ is NOT intended to be a full explanation of all the intricacies of taking and interpreting various prenatal tests, but rather a discussion of them as they pertain to large women. A brief description of the test, its purpose, and the procedures used are given for each test, but the majority of the information is about the specifics of large women and the test. If you need more detail about statistics, interpretation of results, rates of 'false-positives', etc., then be sure to research the many websites devoted to prenatal testing online.

It is also important to realize that most women take these tests without fully considering all of the implications of the test.  Most women think of these as a simple test, a cursory part of prenatal care.  They don't consider that intimately wrapped up in the question of prenatal testing is the moral dilemma of abortion and the thorny issue of eugenics. Barbara Katz Rothman points out: 

The history of prenatal diagnosis has roots in the eugenics movement...part of its history has been an attempt to control the gates of life: to decide who is, and who is not, fit to make a contribution to the gene pool.

Katz Rothman is by no means arguing against the use of prenatal testing; she actually presents a number of compelling reasons to consider it.  Her writing is a fair and balanced look at the intricacies and difficulties of this issue.  

But she has found through extensive interviewing of parents involved in such testing that most of them were simply unprepared to confront the scope of the types of decisions presented by prenatal testing, and that choosing such testing often changed the way a woman experienced pregnancy in subtle ways.

Parents who are considering using prenatal testing need to be sure they really understand the following issues BEFORE the test takes place: 

More on these kinds of questions is available on other websites about prenatal testing, but it vitally important that parents think about these issues BEFORE they decide whether or not to test.

Readers may feel that there is a strong anti-testing bias in this FAQ.  Kmom's own experiences with prenatal testing (detailed in the FAQs) have largely been negative, and she is certainly strongly concerned that so many women enter into these tests without really considering what they are doing beforehand.  

Part of the purpose of this FAQ is to help women understand the scenarios they might face should their screening test come back positive for possible problems.  And because the overall bias of our technological culture is towards doing more and more testing, Kmom feels an extra responsibility to challenge the automatic assumption that more testing is better.  

However, by no means is Kmom condemning testing completely, nor does she criticize those who do choose to test.  Prenatal testing has certain advantages and in some situations can be a great help.  Kmom uses certain types of prenatal testing herself, and under certain circumstances, might choose to use other types too.  She is simply pointing out that the issue is far more complex than most clinicians have patients consider, and that parents need to ask themselves the hard questions before they begin the process.

Finally, it's also important to note that none of these tests are mandatory. Although many women are simply told that they will be taking these tests, it is ALWAYS your right to decline any or all of these tests. Just because you are 35 or over, for example, does not mean that you HAVE to have an amnio, and just because you are a large woman does NOT mean that you have to have the AFP test or gestational diabetes test.  Conversely, it is also your right to request certain tests if they are important to you.  

You have the right to accept or decline any test or treatment during pregnancy. It is YOUR body, and YOU have the ultimate choice. Research the issues carefully so that you make an informed choice, and then either request or decline the test, based on your individual needs and values. Don't let any provider try to bully you into (or out of) tests---listen to their counsel, do your own research, and then MAKE YOUR OWN CHOICES.



Ultrasounds use "sound" waves of extremely high frequencies to help figure out what is going on inside the uterus.  It creates an image by bouncing ultrasound waves off of tissues inside the body (in this case, off of the baby). This creates a flat, two-dimensional image of a three-dimensional baby.  

The ultrasound "transducer" uses crystalline structures to convert electrical energy into ultrasound waves.  These are directed towards fetal structures and "bounce" off of them.  The returning echoes are converted back into electrical energy, which is then translated into a two-dimensional visual picture on a CRT (cathode ray tube) screen. Extra energy is lost or absorbed by the tissues, one safety concern of critics.

Ultrasounds were used for the first time in obstetrics in 1958.  It has come into common use mainly in the last 25 or so years.  It is now done in "real time," meaning that a series of high-speed scans creates the illusion of the baby "moving."  You see the results immediately, as the procedure is being done, and the results change as the procedure continues.  Because the results change so fast, it looks like you are witnessing the baby moving in real time.

There are several different types of ultrasound procedures available, although some newer technologies (such as 3D ultrasound) are not available in all areas.  Which procedure is used with you will depend on many issues, such as how far along you are, why the ultrasound is being done, etc.  

Types of Ultrasound

There are several different types of ultrasound.  The type most familiar to most people is called "B scan" (or brightness modulation), and is used for diagnosing problems in the baby.  It generates discrete pulses of high-intensity ultrasound and listens for discrete echoes back, which are then translated into a two-dimensional picture displayed on a screen.  Although it uses high-intensity ultrasound, this is produced in short quick pulses, so the baby is only actually exposed to a fairly small amount of the high-intensity ultrasound.

Another type of ultrasound is called Doppler ultrasound, which generally uses lower-intensity ultrasound but continuously, instead of in pulses. Instead of producing a picture, it shows the speed and direction of blood flowing through the vessels.  It can be used in several different ways. Most often continuous Doppler is found in the "Doptone" heartbeat monitors (Doppler fetascopes) many providers use during monthly check-ups to monitor the baby's heartrate. It is also used in the Electronic Fetal Monitors (EFM) that many mothers wear continuously during labor to monitor the baby's heartrate. 

Another version of Doppler ultrasound does not use continuous low levels of Doppler ultrasound, but pulsed Doppler instead.  Still another type (called "Duplexing Doppler") combines B-scan ultrasound and pulsed Doppler ultrasound.  Each type has its own uses and advantages.

Sometimes color is added to Doppler ultrasound ("color flow mapping") to help delineate the different areas of blood flow in a pictorial form.  This is especially useful for diagnosing congenital heart abnormalities.  Color Doppler ultrasound is not commonly used in most pregnancies unless there is a specific concern to justify its use.  

All of these different types of Doppler ultrasounds can be confusing.  Anne Freye explains more about the different types of Doppler ultrasound in her book, Understanding Diagnostic Tests in the Childbearing Year.

A sound wave generated by or reflected from a moving object demonstrates the Doppler effect, which consists of a change in transmitted frequency.  Continuous wave Doppler equipment utilizes an emitting crystal and a receiving crystal; the frequencies of the two are compared.  The frequency increases if the object is moving towards the receiver; this is referred to as a positive Doppler shift.  The frequency is decreased if the object is moving away from the receiver--a negative Doppler shift.  The shift in frequency is proportional to the velocity of movement.  This makes continuous Doppler effect unsuitable for imaging but ideal for detecting the motion of the fetal heart.  Doppler fetascopes and external fetal monitors thus generate ultrasound energy continuously at a lower intensity and receive and analyze echoes continuously, often for many hours at a time....

[In pulsed Doppler technology,] a single transducer fires a series of very short pulses and then listens for the echo to measure movement...Duplexing Doppler technology uses a pulse-echo system with a combination of regular B-scan mode and Doppler effect delivered in an alternating pattern...Color Doppler can show dynamic anatomic relationships such as blood flow within an abnormal fetal heart, or a fetal blood vessel otherwise difficult to locate or impossible to visually detect with B-scan imaging.

Most mothers (and even some providers) do not realize that Doptone heartbeat monitors and Electronic Fetal Monitors actually use ultrasound as part of their technology, thus exposing the mother and baby to a great deal more ultrasound in pregnancy than most people realize.  Although these particular Doppler devices use low-intensity ultrasound, the fact that they have continuous exposure worries many critics of ultrasound.   

Considering how often the baby's heartrate is checked with the Doptone during pregnancy, and how many hours many women spend with continuous fetal monitoring during labor, the amount of ultrasound a woman and her baby receive during pregnancy is considerably more than the 15 minutes or so of the routine diagnostic (B-scan) ultrasound done at 18 weeks.  This is one of the many concerns critics have with indiscriminate use of ultrasound technology.  

Methods for Doing Ultrasounds

The two most commonly-used methods for doing ultrasounds are:

  1. Vaginal (or 'transvaginal') ultrasound  
  2. Abdominal (or 'transabdominal') ultrasound

There are other types of ultrasound, and new technologies being developed all the time.  However, information on these is beyond the scope of this FAQ.  You can find out more about them at

Transvaginal Ultrasound

Vaginal ultrasound is used for very early pregnancy, and sometimes for heavier women with more abdominal fat. This type is done trans-vaginally, using a long 'wand' (transducer) that is covered with a condom (!), lubricated, and placed inside the vagina. A male technician may ask you to insert it yourself (a female attendant should also be present in these cases, or you can request ahead of time to have a female technician instead). 

The 'wand' is then moved around your vagina to allow the technician to 'see' up into the uterus and abdomen as needed. Occasionally it needs to be pressed up on either side of your cervix firmly to 'see' the ovaries clearly, which can be a bit uncomfortable for some women, but the discomfort is usually tolerable. Some moms have likened a transvaginal ultrasound to 'having someone driving a stick shift inside.' That’s a crude but accurate description. Having a sense of humor about it makes it easier.  However, women who have sexual abuse background may want to request a female technician instead or avoid having an early ultrasound altogether, depending on their comfort levels.  

Generally speaking, the trans-vaginal ultrasound is used in the first trimester, since the uterus has not yet grown big enough to lift out of the pelvic cavity. It is very useful in getting a clearer picture to determine whether there is an ectopic pregnancy, whether the fetus is viable, if there are multiple fetuses, etc.  It is especially useful in heavyset women and perhaps in women with a retrograde uterus.  

Because the transducer is right up by the cervix and thus right next to the baby, the ultrasound waves do not have to go through the abdomen before reaching the baby, and the picture is often clearer than with an abdominal ultrasound at this point.  However, it also means the transducer is much closer to the baby than with an abdominal ultrasound, and critics worry about the safety of this.  Does the baby receive increased levels or intensity of ultrasound this way, and is this more harmful particularly because it is usually used during the first trimester?  No one knows.

The closeness of the trans-vaginal transducer (and its ability to use somewhat higher frequencies) is a particular advantage in the case of very heavy women with extensive abdominal adiposity.  Although abdominal ultrasounds definitely work on heavy women later on in pregnancy, sometimes they are not very effective earlier in pregnancy.  Thus transvaginal ultrasounds are especially common in women of size early in pregnancy. However, it is also not unusual for women of all sizes (not just heavy women) to have difficulty getting a clear abdominal ultrasound early in pregnancy, so big moms should not feel like they are the only ones having a vaginal ultrasound.  When ultrasounds are done in very early pregnancy, they are usually done transvaginally.  It is only a little later that there is a difference in ultrasound method due to size and this does not last for long.  

At some point around the end of the first trimester, most average-sized women can have an abdominal ultrasound done, but in some larger women, a transvaginal ultrasound may still need to be used for a few weeks yet in order to get a more effective picture. However, every woman is different and many larger women have reported being able to use an abdominal ultrasound at about that time too. Each case will be different and has to be decided at the time, but be aware that transvaginal ultrasounds may have to be used just a bit longer in larger women.

Transabdominal Ultrasound

The second type of ultrasound (abdominal) is the type commonly seen on TV shows. It uses a kind of 'mouse' (transducer) attached to a computer and view screen. Warmed lubricant jelly is placed on your belly and the transducer is applied---where on the belly depends on the stage of your pregnancy. 

The technician then moves the transducer around as needed to 'visualize' your fetus, its organs, your placenta, your ovaries, and possibly your cervix.  They also usually measure certain key parts of the fetus to help estimate the baby's age, including: 

Different methods are used to estimate the baby's age or fetal weight (see below) and there is great debate in the ultrasound community over the efficacy and relative merits of each method.  Keep in mind that results can differ based on the method used, the skill of the sonographer, and the relative position of the baby.  Therefore, take such estimates of fetal age or weight with a big grain of salt.  They are not known to be terribly  accurate most of the time.  

Doctors usually request that you drink a lot of water before an early abdominal ultrasound in order to help produce a better picture. A full bladder also  helps lift the uterus up out of the pelvic cavity so it can be seen more easily.  Since many women report drinking a ton of water, then having to wait for their ultrasound with the discomfort of an overly full bladder, be sure to ask how much water is really necessary! 

Sometimes drinking a lot of water is not absolutely necessary for some ultrasounds, or they may require less water than you think. Generally, drinking lots of water is more important in very early abdominal ultrasounds and in scans that need much more detail.  Later ultrasounds usually don't require nearly as much water consumption.  Ask ahead of time how much is needed; no need to suffer bladder distension if it's not needed!

In the beginning of pregnancy, if an ultrasound is deemed necessary, it is usually done transvaginally.  As a woman's pregnancy progresses, the abdominal ultrasound is usually used instead, commonly sometime after the first trimester. As noted above, the transvaginal ultrasound may need to be used a bit longer in women of size, but eventually women of all sizes are able to have an abdominal ultrasound just fine.  

Although many heavy women fear that their abdominal fat will prevent the technician from "seeing" anything with the ultrasound, this fear is unfounded.  Rest assured, the ultrasound technician WILL be able to see your baby eventually, even if you are very heavy around the middle. They may need to use the vaginal ultrasound a little bit longer because of size, but eventually every large woman is able to have an abdominal ultrasound, no matter how big she is around the middle.  Fat will not prevent an ultrasound!

However, extensive adiposity can sometimes make it harder to see everything thoroughly.  The area that tends to be most difficult to see in big women is the baby's heart, and sometimes the baby's spine, the mother's ovaries, and the baby's kidneys or urinary system as well.  Please note that most of the time, these are seen without problem in women of size, but that sometimes a repeat scan may need to be done.  Rest assured that there ARE techniques that can help get a clearer image in women of size, and that most of the time, questions about the baby's health or structure are able to be resolved satisfactorily in women of size too.

"Level Two" Ultrasound

Sometimes a doctor will use the term, "Level Two Ultrasound" and women are uncertain what that means.  Do they use stronger ultrasound machines, a different type of ultrasound, different imaging techniques, or what?  

The answer is that a Level Two Ultrasound is really no different that any other ultrasound, it simply looks more thoroughly.  Instead of a superficial "look" at the fetus, a Level Two ultrasound looks specifically for any suspected problems or areas of concern.  The term really only means a longer and more in-depth ultrasound, sometimes referred to as a "targeted" ultrasound. 

Other Common Sources of Ultrasound in Pregnancy

As noted above, many women don't realize that there are other sources of ultrasound during pregnancy besides having the traditional ultrasound scan for diagnosing problems.  "Doptones" (Doppler fetascopes) are the little machines that most providers use every month to listen for fetal heart rates.  Some providers don't even realize that these involve the use of ultrasound!  And few women realize that the "Electronic Fetal Monitoring" (EFM) belts that many women have on during labor and Non-Stress Tests are actually also using ultrasound to continuously monitor the baby's heart rate. 

Although most doctors are very unconcerned about the safety of this, many in the "alternative" birth community are greatly concerned about the safety implications of this much ultrasound. Because there is limited information on this issue, this FAQ will focus more on the ultrasound scans commonly used in pregnancy for prenatal diagnosis (B-scans). However, considering the amounts of ultrasound women experience through Doptones during their routine check-ups, and the hours and hours they are exposed to with EFM during labor, it is an issue ripe for MUCH more exploration.

Ultrasound Type Summary

So in summary, there are several different types of ultrasound technology in use today, and many new types are being developed.  "B-scans" use pulsed high-intensity ultrasound waves to help diagnose fetal problems; this is the technology most people think of when they picture having an ultrasound.  This is the technology most of this FAQ is concerned with.

Doppler ultrasound uses continuous low-intensity ultrasound to help keep track of the fetal heartrate, among other things.  It is used in Doptones and Electronic Fetal Monitoring, although many women don't realize these employ ultrasound technology.  

In addition, there are several other types of ultrasound, including pulsed Doppler technology, and Duplexing Doppler technology, which combines pulsed Dopplers with B-scan technology.  Color Doppler does not show color pictures of the baby, but uses superimposed colors to help show blood flow more clearly in fetal structures like the heart.  In addition to these forms of ultrasound technology, there are other forms, both older and newer.  However, for the most part, this FAQ concentrates only on B-scan ultrasound technology.

There are two main methods for doing ultrasounds today---the transvaginal ultrasound, and the transabdominal ultrasound. The transvaginal is used early in pregnancy because it gets closer to the baby with less intervening tissue, and is thus able to get a better image early in pregnancy.  It is also used sometimes with heavier moms in the beginning of the second trimester.

The transabdominal ultrasound is the type you see all the time on TV.  By 16-20 weeks, when most providers request a routine ultrasound scan, women of all sizes are usually able to have a transabdominal ultrasound with very few problems.  Transabdominal ultrasound is the most common kind of ultrasound used today in obstetrics.  

Although practitioners sometimes refer to a "Level II" ultrasound, this is simply a longer and more detailed ultrasound to look for specific concerns, not a different type of ultrasound technology.  It is done if there are special reasons to suspect possible fetal problems (such as diabetes or a family history of birth defects),  if a prior ultrasound has shown a possible problem, and as a routine step before special procedures like amniocentesis.  

Other sources of ultrasound that women often encounter during pregnancy include Doptones (to listen for fetal heart rate), and Electronic Fetal Monitoring (to monitor baby's heartbeat continuously during labor).  However, these devices use a different type of ultrasound technology, and some sources feel that this may pose a bit more risk to the baby.  More information is needed.

There are new technologies coming out in the field of Sonography, such as 3D ultrasound and more. However, at this time its use is uncommon, and little data exists on its efficacy, utility, or safety.  Stay tuned for more information.  


Safety Issues

Most practitioners consider ultrasounds perfectly safe, and strongly dismiss the concerns of anyone who questions this.  However, there is a small but vocal minority of critics that contend that ultrasound safety is unproven and should be approached with more caution.  

These critics oppose routine ultrasound with no clear indications for use, and generally believe that ultrasounds should only be used when their potential benefits clearly outweigh any potential risks.  Other critics are not opposed to one routine ultrasound during pregnancy but are leery of the vastly increased number of ultrasounds being done today, especially with today's more powerful machines.

The point is that there are still safety concerns over ultrasound use, particularly with the newer technology.  While there is no "smoking gun" set of studies that prove beyond a reasonable doubt that ultrasound is unsafe, there are still many questions that remain to be answered.  Some caution seems to be prudent.  

The Basic Issues

This FAQ cannot fully cover the concerns over the safety of ultrasound; this is a major issue, not easily or briefly discussed.  There are other websites available which discuss the issue much more thoroughly, and there is no need to duplicate this work here.  

However, this FAQ can summarize the basic concerns of many critics (as expressed in the book, Ultrasound? Unsound from the Association for Improvements in the Maternity Services [AIMS] coalition in the United Kingdom).  These include:

  1. "Scans which were originally intended for women with potential problems are now given to almost every pregnant woman and are part of routine care.
  2. There is no adequate evidence that this is beneficial and huge resources are involved.
  3. The number of scans per baby has increased--some members report nine or more.
  4. The machines have become more powerful and there is inadequate information or control on levels of output.  
  5. Many scans are being carried out by staff who are poorly trained and do not understand potential risks and how to minimise them.
  6. Scans are being used on more women in very early pregnancy when major organs are being formed.
  7. With the development of the vaginal probe the ultrasound now gets nearer to the baby with less intervening protective tissue.
  8. There is more use of Doppler ultrasound (which may carry greater risk) to study blood flow in the uterus and the baby.
  9. Some clinicians and researchers are exposing women and babies to long periods of ultrasound--an hour or more."

Note that the AIMS coalition does not condemn all ultrasounds.  They merely urge caution in its use, and call for further research into its safety.  They state, "One cannot talk about risk or benefit for scanning as a whole.  Risks and benefits are likely to be very different for different types of ultrasound, different stages of pregnancy, different machines, different centres, different sonographers and different conditions in pregnancy."  

In other words, in some situations, under certain conditions, ultrasound's potential benefits probably outweigh its potential risks.  In other situations, however, it may not.  Each situation must be judged on its own merit; don't just agree to an ultrasound automatically, without really understanding what it is for and whether there are any real benefits to doing it.  

The debate over ultrasound safety is viewed as moot by most medical professionals.  Many feel there is no question that ultrasound is safe in all instances, no matter when it is used in pregnancy or for how long.  Dr. Marjorie Greenfield of, for example, states outright, "Ultrasound in its current form seems to be completely safe for the fetus.  No risks have been demonstrated in its 25 years of common use."

However, this is not quite accurate.  There have been studies that have pointed out some safety concerns, including an increase in premature labor, miscarriage, growth-retarded fetuses, perinatal deaths, more left-handedness, more delayed speech, and more learning disabilities.  (See the websites listed below for complete references.) These are significant concerns and should not be shrugged off lightly.  

But it is also true that further review of studies that found problems has questioned their conclusions, their small size, their many confounding factors, and the difficulty others have had replicating the results.  As noted at  

There have been many concerns about the safety of ultrasound. Because ultrasound is energy, the question becomes "What is this energy doing to my tissues or my baby?" There have been some reports of low birthweight babies being born to mothers who had frequent ultrasound examinations during pregnancy. The two major possibilities with ultrasound are as follows:

However, there have been no substantiated ill-effects of ultrasound documented in studies in either humans or animals. This being said, ultrasound should still be used only when necessary (i.e. better to be cautious).   [underline emphasis Kmom's]

By no means does Kmom believe that all safety concerns with ultrasounds are proven facts, but neither is it true that 'no risks have been demonstrated,' either.  There IS still room for concern, especially as the technology expands into new and more powerful forms, and as babies are exposed to earlier and more frequent scans.  More research is needed, and more long-term follow-up is especially important. 

Some doctors have expressed concerns over ultrasound safety.  Dr. Sarah Buckley expresses major concerns in her article, "Ultrasound Scans: Cause for Concern,"  which can be found online at  In this article, Dr. Buckley reviews ultrasound research, pro and con, and the value of routine prenatal ultrasound.  As a result of her research, Dr. Buckley and her partner (also a doctor), chose not to have ultrasound scans in her four pregnancies, but also presents guidelines for those women who do choose to have ultrasounds during their pregnancies.  

An excellent website discussing concerns over ultrasound safety is  It reviews a great deal of research about ultrasound safety issues, points out concerns with many of the studies that found problems, and concludes that ultrasound is basically safe.  However, it does include a few cautions:

Available data in the literature do not indicate any specific risks of physical damage arising from the use of ultrasound. Cavitation can be produced in vitro by ultrasound but there is no evidence that it can cause human damage in vivo. Microstreaming is an uncertain phenomenon in vivo and may, in any case, not be damaging. Thermal effects are perhaps those of greatest concern and precautions must ensure that significant temperature rises are avoided in practice. Particular care should be taken in certain clinical circumstances, for example early pregnancy, and with ultrasound modes such as pulsed Doppler.

The meta-analyses of randomised controlled trials of adverse effects show only that there is a just significant increased tendency to non-right handedness in the offspring of women who had scans; the complexity of the study makes the observation difficult to interpret. Nevertheless continual vigilance is necessary particularly in areas of concern such as the use of pulsed Doppler in the first trimester.

The greatest risks arise from the use of ultrasound by inadequately trained staff, often working in relative isolation and using poor equipment. Ready referral to a tertiary centre for further advice, usually from a multidisciplinary team, is an essential feature of the screening process ....

This site brings up the important point is that if possible, it is better to do an ultrasound in a major center that specializes in prenatal ultrasounds.  The ultrasound techs there are more likely to be better trained and the machines more powerful.  

This may sound like a contradiction for those concerned about ultrasound safety-----choose to go to a center with more powerful ultrasound machines? But there the images will be gotten so quickly there will be less need for long and/or repeat scans.  The techs will be more likely to be experienced and trained in ultrasonography, so they'll know all the "tricks" for efficiently getting a good image. As the AIMS coalition notes: "A properly trained sonographer can obtain the necessary information from the scan more quickly, thereby reducing exposure to the baby." 

Anne Freye, in her book Understanding Diagnostic Tests in the Childbearing Year, also discusses the concerns that many critics express over the current extensive use of ultrasounds in pregnancy.

The three main types of ultrasound diagnostic devices each present separate theoretical risks.  If it were found that the total duration of ultrasound exposure is a critical factor, then the external fetal monitor could prove to be most dangerous (in many cases exposure during labor may exceed 10 hours).  

If gestational age is critical, early scans and the use of Doppler fetascopes and [intravaginal] probes may prove most harmful.  If there is a sensitive period early on in gestation, the focused beam of the [intravaginal] probe may hit it.  If there is a sensitive organ or target area in the fetus, then a diagnostic imaging scan may be the most dangerous since the entire fetal body would be exposed....

What if damage results after cumulative exposure?  If so, those babies who are most likely to experience problems anyway, such as those seen as candidates for serial exams, are at most risk.  If bone is becoming overheated, then the rapidly and constantly developing fetal brain, encased as it is in bone, is especially at risk for damage.  Is this why so many studies suggest neurologic impairment from exposure?

The question of maternal effects is also not being addressed.  The mother's and her female fetus's ovaries are irradiated during an ultrasound scan, bringing up the question of possible chromosomal damage....

In summary, studies often done in animals or tissues in laboratories and often using larger doses than those used in humans have noted the following affects:

Other studies have refuted some of these claims.  Some studies are cited as being too small or having too many confounding factors to draw any useful conclusions.  It is difficult to know what to believe....

At another point in her book, Freye continues:

Today, millions of ultrasound exams have been performed and millions of babies have been exposed during pregnancy.  Without dramatic birth defects to stop its use, more subtle biological sequela may go unrecognized for years to come.

The excellent book, A Guide to Effective Care in Pregnancy and Childbirth by Enkin et al., is a medical evidence-based review of obstetric care issues, often in conjunction with the highly recognized Cochrane Pregnancy and Childbirth Database.  Reviewers analyze huge numbers of studies and create a meta-analysis of research data about these issues.  The third edition (2000) of the book concludes the following about the potential hazards of obstetric ultrasound:

Any consideration of the use of diagnostic ultrasound in obstetrical practice must weigh potential benefits against potential risks.  There has been surprisingly little well-organized research to evaluate possible adverse effects of ultrasound exposure on human fetuses.  Based on the available follow-up of children included, as fetuses, in randomized trials, there is no evidence of a greater risk of impaired school performance at age 8-9, or of dyslexia, following routine imaging ultrasonography during the second and third trimesters of pregnancy, but there are suggestions (perhaps a chance finding) of an increased incidence of left-handedness.  

Two apparently well-designed and well-conducted case-control studies have sought a relationship between ultrasound exposure and childhood malignancy.  Both were reassuring, with one possible exception: neither study showed any difference in exposure between the cases and controls up to the age of 5, but in one of the studies, children dying of leukaemia or cancer over the age of five were more likely to have been exposed to ultrasound as fetuses.  This difference was not seen in the other, statistically more powerful study.

There has been a suggestion of more growth-restricted babies born after repeated ultrasound examinations during pregnancies in one human study, although differences were no longer evident at one year of age, and this may have been a chance finding.  The randomized, controlled trials conducted to date have been far too small to have a reasonable chance of identifying an effect of ultrasound exposure on any rare adverse outcome...At present, there is no sound evidence that ultrasound examination during pregnancy is harmful. 

As noted, a truly thorough discussion of the safety and/or risks of ultrasound is well beyond the scope of this FAQ.  Women are urged to do their own research.  Further discussion of the issues can be found in Understanding Diagnostic Tests in the Childbearing Year. Online, further discussion of the ultrasound controversy can be found at the following websites:

A Cautionary Tale

As noted, most medical professionals believe that ultrasound is perfectly safe in any form, under any conditions.  They strongly dismiss critics' concerns about its safety. However, just because most doctors consider ultrasound totally safe doesn't mean that it automatically is safe.  The history of obstetrics is RIFE with stories of technology or drugs accepted as safe and put into widespread use, yet later found to be tremendously harmful.  Acceptance by doctors does not necessarily guarantee safety.

For example, before ultrasound really came into use, doctors in the 1950s used X-rays on pregnant women to determine the baby's position, etc.  In 1956, Dr. Alice M. Stewart, an epidemiologist with Oxford University, published a study on children who had been exposed to prenatal X-rays.  She found that the children of mothers who had had these X-rays were almost twice as likely to have cancer as other children. 

Dr. Stewart's findings were met with outrage from her colleagues of the day, and she had great difficulties finding financing for other studies. Most OBs of that time period would have said that prenatal X-rays were perfectly safe. Yet they were not, and proof that they were unsafe was routinely discredited for many years. It is typical of obstetrics that it took about twenty years for her findings to be taken seriously. In the 1970s, her findings were duplicated by other scientists, and the use of prenatal X-rays largely ended (although they are still used to a small extent even today).  How many babies became ill or even died in the 20 years it took for scientists to take these concerns seriously?  

Now obviously, this is an extreme case.  No one believes that ultrasounds are as dangerous as prenatal X-rays. But the point is that many things in obstetrics are adopted without fully studying their safety and efficacy, and the safety concerns of critics are often ignored for years, harming many babies in the meantime.  X-rays is but one example; others include the "twilight sleep" drugs used during birth for many years, aggressive use of forceps and fundal pressure during birth, drugs such as DES and thalidomide, and many others.  History proves that just because doctors say something is safe doesn't mean it is, and this has been especially true in obstetrics. 

Neither does it mean that ultrasound is not safe or should never be used.  It simply means it should be used with more caution, and that further research into safety issues should continue.  Women should know of the possible concerns with ultrasound and should not treat them lightly.  Because ultrasounds are so emotionally rewarding to have, many women are seduced into requesting multiple ultrasounds, sometimes even monthly ultrasounds, for no valid medical reason.  

And now there are "baby heartbeat monitors" available for home use.  These use ultrasound to let the parents "listen in" on the womb, and check the baby's heartbeat to reassure themselves that all is still well within.  Who could resist that?  But the problem is that these home heartbeat monitors are greatly increasing the baby's exposure to ultrasound, and no one knows what the possible effect of such long and frequent exposure would be.  What may be relatively harmless done once or twice in pregnancy for short periods may be something completely different done an hour a day, every day, for nine months.  

Because of these new technologies, it is important to remind women that there are still safety concerns with ultrasounds, that routine ultrasounds have not been proven to have any medical benefit, and that new technologies may not have adequate safety testing yet to fully know their health implications.  Because babies in utero are potentially so vulnerable, women should not to take ultrasound scans lightly.  

Kmom's Opinion

So what is a mother to do?  How is she to know whether to have ultrasounds or not?  This is not an easy question.  Kmom is not a doctor nor an ultrasound expert, but the following seem to be logical conclusions to her, based on the research. Caveat Emptor; take these opinions with a grain of salt and remember that NO medical advice is implied. Each woman should consult with her provider, research the issues herself, and then decide what the best course is for HER own situation.   

In Kmom's personal opinion, ultrasound is probably not a cause for great concern if used reasonably.  Based on the evidence available, most mainstream research on ultrasound does seem to support that limited amounts of traditional ultrasound are relatively safe if care is taken, if the technician is well-trained and highly skilled, if the appropriate machine is used, and if exposure is limited as much as possible. Women should probably not worry too much about limited use of diagnostic ultrasound.

However, questions do remain about ultrasound safety. Most ultrasound safety trials looked for obvious defects or problems, such increased cancer rates, major learning disabilities, miscarriages, obvious growth restriction, malformations, etc. (Indeed, some studies found some of these problems, but the results were not able to be replicated by other studies.)  It seems clear from the preliminary research on technologies of the past that limited use of ultrasound is unlikely to result in significant and obvious problems.   

However, this does not rule out the possibility that major exposures to ultrasound can cause more subtle or rare problems.  As Enkin et al. state, "The randomized, controlled trials conducted to date have been far too small to have a reasonable chance of identifying an effect of ultrasound exposure on any rare adverse outcome."    Frye echoes this concern by saying, "Without dramatic birth defects to stop its use, more subtle biological sequela may go unrecognized for years to come."  While no obvious, gross problems seem to be conclusively caused by ultrasound, subtler problems may go unstudied and undetected.  

One very strong concern about ultrasound safety is the lack of data on the newer technologies now being used.  More information is needed about the use of pulsed Doppler, the use of ultrasound in the first trimester, the safety of vaginal ultrasounds, and the effect of multiple extensive scans, not to mention the extensive use of Doptones and Electronic Fetal Monitoring.  

Because ultrasound technology is evolving and becoming more powerful, research should continue into ultrasound safety, especially as it evolves with new technology and greater amounts of exposure.  Unfortunately, such research is limited, and long-term studies are lacking. Most doctors and researchers assume that because past ultrasound technology used in a limited way seems relatively safe, that means all ultrasound technology must be safe, no matter what type it is, how it is used, when it is used, and how often or long it is used.  This is a dangerous extrapolation. In this area, new technology is rapidly evolving and being adopted into general use before complete data on its safety is being documented.

Therefore, it is probably best not to overuse ultrasounds unnecessarily.  Some doctors order monthly ultrasounds, even in uncomplicated pregnancies, and in Kmom's opinion, this is probably not a good idea. Ultrasounds should be restricted to those which are truly medically indicated, show clear benefit of use, and should be done only by highly trained sonographers using sophisticated machines.  

In Kmom's opinion, women should also probably avoid the "home" baby heartbeat monitors, as this likely gives the baby a great deal of unnecessary exposure, and we simply don't know what the effects are of so much exposure.  If a woman is determined to have one of these, she should probably use only very infrequently, just in case.  Avoid the temptation to listen every day----but better yet, avoid them entirely.  Limit your ultrasound exposure to only the medically necessary procedures.

Although ultrasounds have never been proven conclusively to be harmful, neither have they been proven to be harmless. They are simply a useful tool under some circumstances in pregnancy, but should not be abused through overuse since we have no proof of their lack of harm, nor of benefit to their routine use.  At this time ACOG (American College of Obstetricians and Gynecologists) and a National Institute of Health consensus development conference recommend ultrasound only for a specific medical indication; they do not recommend the routine use of ultrasound screening during pregnancy.  Unfortunately, most doctors ignore this recommendation.


The Utility of Ultrasound

How useful is ultrasound scanning, really?  Because doing so many ultrasounds ties up healthcare dollars that could be used elsewhere, and because ultrasound does pose some theoretical safety concerns, the utility of ultrasound is important to consider in  public health policy.  

In some cases, there is no question that ultrasound scanning is highly useful and effective.  If you have an ectopic pregnancy, it is to your great advantage to discover this right away so that danger to your fertility and your life is minimized.  For very specific medical concerns like this, it is obvious that ultrasound is worth the resources devoted to it and any possible safety tradeoffs. 

On the other hand, routine ultrasound scans have become the norm in the second trimester of pregnancy in the USA, costing millions of dollars, yet the utility of this routine use of ultrasound has been strongly questioned.  Is routine ultrasound clinically justified?  This question is much more difficult to answer. 

The RADIUS trial (New England Journal of Medicine, 1993) found that routine screening in the second and third trimesters did not improve perinatal outcome, not even for women with multiple gestations, small babies, post-date pregnancies, or those whose babies were diagnosed with congenital anomalies. The authors concluded, "Screening ultrasonography did not improve perinatal outcome as compared with the selective use of ultrasonography on the basis of clinical judgment." 

The following is an excerpt from a summary of the debate over the utility and possible benefits of ultrasound, as found in the textbook, Guide to Clinical Preventive Services, Second Edition.  The chapter is called "Prenatal Disorders: Screening Ultrasonography in Pregnancy."  It is posted online at   

Routine third-trimester ultrasound examination of the fetus is not recommended. There is insufficient evidence to recommend for or against routine ultrasound examination in the second trimester in low-risk pregnant women....

Neither early, late, nor serial ultrasound in normal pregnancy has been proven to improve perinatal morbidity or mortality. Clinical trials show that a single midtrimester ultrasound examination detects multiple gestations and congenital malformations earlier in pregnancy, but there is currently insufficient evidence that early detection results in improved outcomes. In the U.S., it is not clear whether early detection of fetal anomalies by routine ultrasound leads to increased rates of induced abortion. In addition, many of the major fetal anomalies discoverable by routine ultrasound might be detected anyway during screening for Down syndrome....

Routine second-trimester ultrasound can lower the rate of induction for presumed postterm pregnancy, a benefit likely to accrue primarily to women with unreliable dates, among whom ultrasound is more accurate than dates for predicting actual date of delivery. Early ultrasound has not been proven to reduce overall rates of induction, however, due to increases in inductions for other indications. It is also unclear whether the likeliest potential benefits of routine second-trimester ultrasound (reduced induction of labor for postterm pregnancy and increased induced abortions for fetal anomalies) would justify the significant economic implications of widespread testing. 

No benefits of routine ultrasound examination of the fetus in the third trimester have been demonstrated despite multiple randomized controlled trials. Additional trials of third-trimester placental grading are needed to adequately evaluate the potential benefits of screening for placental appearance. Further research to evaluate possible adverse effects of ultrasound and the cost-effectiveness of routine screening is also needed.

Routine ultrasound examination of the fetus in the third trimester is not recommended, based on multiple trials and meta-analyses showing no benefit for either the pregnant woman or her fetus ("D" recommendation). There is currently insufficient evidence to recommend for or against a single routine midtrimester ultrasound in low-risk pregnant women ("C" recommendation). These recommendations apply to routine screening ultrasonography and not to diagnostic ultrasonography for specific clinical indications (e.g., follow-up evaluation of elevated maternal serum a-fetoprotein)....

[The draft update of this chapter was prepared for the U.S. Preventive Services Task Force by Carolyn DiGuiseppi, MD, MPH, based in part on materials prepared for the Canadian Task Force on the Periodic Health Examination by Geoffrey Anderson, MD, PhD.]

Despite the fact that ACOG and many authors have pointed out the lack of research justifying the routine use of ultrasound, most OBs (and even nurse-midwives) in the USA still order ultrasounds for most pregnancies.  

One major factor is that ultrasound has become an incredibly lucrative source of revenue for hospitals, one which they are loathe to give up.  And of course, the move towards ultrasounds is consumer-driven as well; the emotional rewards of "seeing" the baby in utero results in most women demanding not just one but multiple ultrasounds in pregnancy.  Thus, although the benefits of routine ultrasound are dubious, it will no doubt continue to be considered a 'standard' part of pregnancy. 

However, ultrasounds are not a required part of pregnancy.  Women can and have declined routine ultrasound in their pregnancies, and it is perfectly reasonable to do so if desired.  Conversely, women who desire routine ultrasound should rest assured that they will almost certainly be able to indulge this wish as well, and in all likelihood the risks from doing these ultrasounds will not be large.  

Ultrasound will no doubt remain part of standard obstetric care for some time to come.  For specific medical concerns this is no doubt justified. Whether it is justified for routine ultrasounds is dubious, but it will almost certainly continue to be done anyhow.  However, always remember that women DO have the ultimate choice as to whether or not to use this technology in this way. 


Accuracy of Ultrasounds

How accurate are ultrasounds?  If you are told your baby appears normal, will this always be true?  Or if you are told that your baby has major problems, will this always be true?  How likely is it that the results you will be given will be right or wrong?

The answer is that like any prenatal testing, ultrasound results are not always correct.  There are "false positive" results (where a baby is wrongly diagnosed as having a problem) and "false negative" results (where the ultrasound results appear normal but the baby actually does have a problem).  Keep in mind that it is never possible to be 100% sure about prenatal testing results.  

It is very clear from the research that the effectiveness of the ultrasound depends greatly on the quality of the equipment used and the skill of the technician using it.  There are very clearly more "false positives" and "false negatives" from ultrasound technicians who have not received special training in the use of ultrasonography, or from those who are using a less-powerful machine.  

Some providers can do basic ultrasounds in their office, but the accuracy of these is limited.  In addition, consumer health advocates have found that many technicians and doctors are inadequately and inconsistently trained in using ultrasound.  Both American Baby magazine and the Wall Street Journal have done articles on the lack of training of many ultrasound techs and docs and the problems this can cause.  You can read these articles at and  

For example, reports that one insurance company required obstetricians to pass a certification program in using ultrasound, due to concerns over poor quality of ultrasound imaging.  Only 36% of OBs passed the test.   The problem is that in the past, many OBs rushed out to buy ultrasound equipment without actually having truly adequate training in using and analyzing the results.   

Finances are a big factor.  The Wall Street article noted above quotes Roy Filly, Professor of Radiology at UCMC in San Francisco as saying, "Sonography is rife with virtually untrained practitioners who are treating this imaging tool like an open cash register drawer."  Most women are begging for more ultrasounds, an OB can do one quickly in his office, and then he can bill for it handsomely.  Ultrasounds have become big business, and help support the less lucrative parts of obstetrics. According to, the price of this is accuracy.  Its analysis of the famous 1993 RADIUS study points out:

The most important conclusion from the RADIUS study is that if the ultrasound examination is performed by obstetricians, community-based radiologists, or their technicians, over 85% of major birth defects and virtually all (99%) serious heart defects are missed!  This is due to lack of experience of the physician who must divide his or her clinical activities among many different areas, thus precluding the necessary time required to develop expertise in this part of medicine.  

When in doubt, choose a facility that specializes in ultrasounds and be sure the technician or doctor is well-trained in performing ultrasounds.  This improves the accuracy of ultrasounds significantly, and is particularly important in the detection of fetal abnormalities.

The following is a summary of the accuracy of ultrasound, as found in the textbook quoted above, Guide to Clinical Preventive Services, Second Edition, located at   Full references for the studies cited below are available from that site.  

Many fetal structural malformations, including cardiac, gastrointestinal, renal, limb, and neural tube defects, can also be detected by current ultrasound techniques...Detection rates depend on the quality of the equipment and the expertise of the ultrasonographer. In a trial in low-risk pregnant women, routine serial ultrasonography at 15-22 and 31-35 weeks of gestation had a sensitivity of 35% for detecting fetuses with at least one major anomaly before delivery but only 17% for detection before the typical gestational-age limit for legal abortion (<24 weeks)...In this study, the sensitivity of routine midtrimester ultrasound was significantly higher at tertiary compared to other scanning facilities (35% vs. 13%). 

Diagnostic ultrasounds are considerably more accurate for certain fetal abnormalities than for others.  For example, most cases of anencephaly are found on prenatal ultrasound.  Cases of spina bifida are a little harder to find, and cases of minor defects like cleft palate are often missed.  Again, much depends on the expertise of the sonographer and the quality of the machine used.  

One major concern parents have is the possibility of a "false positive" diagnosis, or being told there was a problem when in actuality there was not a problem.  Although rare, this does happen, and it is more common from "office" ultrasounds.  As noted below, it is less common in "tertiary facilities" (major facilities with extensive ultrasound equipment and specialists).  

[From the same site, discussing the same study cited above] False-positive diagnoses were reported for 7 cases, or 0.9/1,000 pregnant women scanned before 24 weeks, with most reported from other than tertiary facilities. 

In another trial, the rates of detection of major malformations by screening before 20 weeks (confirmed at abortion or delivery) were 36% and 77% at two hospitals...Ten of the thirty cases with suspected major malformations were judged normal at follow-up ultrasound examinations at 20- 36 weeks and an 11th was found to have only a minor anomaly at delivery; 2.7/1,000 pregnant women received a false diagnosis of a major fetal malformation. 

Large case series evaluating routine ultrasound in low-risk women have reported sensitivities ranging from 21% to 74% for detecting major fetal abnormalities prior to 22-24 weeks among women who were scanned in the second trimester...False-positive rates of 0.2-1.0/1,000 women scanned were reported; in one study, 6 of 8 initially false-positive diagnoses were corrected on follow-up evaluation. Direct comparisons of the trials and series results are hampered by varying definitions of "fetal malformation."

In summary, it is important to remember that ultrasound does NOT detect all birth defects; in some places, it does not even detect most birth defects.  If you have an ultrasound and everything looks 'normal,' that is very reassuring and a good sign but keep in mind that is not a guarantee.  

It is also important to emphasize that sometimes ultrasounds incorrectly identify a fetus as having a major malformation, when in fact the baby was normal or the birth defect was minor.  Although this is quite rare, it does happen.  Therefore, always get a second opinion (or more) if problems are diagnosed via ultrasound.  

There have been cases where a birth defect or other problem was diagnosed with ultrasound and the baby was later found to be normal (see Jessica's Story, below, and  There have even been cases documented where a baby was diagnosed with a birth defect and aborted, and the postmortem exam found the baby to be perfectly normal (see Ultrasound? Unsound and Understanding Diagnostic Tests in the Childbearing Year).  Although this is extremely rare, it has happened and is devastating.  Remember the weaknesses of ultrasound and be wary of any drastic actions based on its results.  

Also remember that most office ultrasounds are less sensitive than the machines used by ultrasound specialists and perinatologists, so especially beware jumping to conclusions based on a scan from one of these less-effective machines.  For example, a heartbeat very early in pregnancy might well be missed on an office machine, so beware of concluding too quickly that there was a miscarriage and having a D&C.  Although one must weigh all the potential risks and benefits, many women choose to wait a while longer and/or have another scan before deciding what to do.  [See Christine's Story, below.]

If there is any kind of a question about the baby's health or status, get another ultrasound from a center that specializes in prenatal ultrasounds.  If there are any serious health implications of the results, ask to see a perinatologist.  They are the experts in pregnancies with potential problems, and they have more training and experience in these issues.  Be sure they are well-trained in ultrasound diagnosis, know the potential pitfalls of ultrasounds for diagnosis, and use a really top-notch machine.  If in doubt, don't be afraid to ask for even another opinion from another perinatologist.  Better safe than sorry.

Although ultrasound can be extremely useful and even life-saving at times, remember that it is not a perfect technology.  Like all technologies, it can be very useful at times, but its use can also lead to problems if used inappropriately.  Its accuracy is only as good as the training of the people using it and the quality of the machine being used, and even under the best of conditions, it is not 100% accurate.

In general, ultrasounds are more accurate when done on more powerful machines and by people who are highly trained and very experienced in their use.  If you are going to have an ultrasound, it is probably best to be very cautious about results from 'office' ultrasounds and whenever possible, opt for ultrasounds at a tertiary center that specializes specifically  in ultrasounds.  Even then, there is no guarantee of the accuracy of the results.  Be cautious about taking any drastic action based on such results. 


Reasons for Doing Ultrasounds

Reasons for doing an ultrasound vary greatly. Early in pregnancy, they may be used if an ectopic pregnancy is a possibility, to determine if the fetus has died, if twins are a possibility, etc.  Because the baby's major organs and systems are being formed at this time, it is probably better not to do an ultrasound in early pregnancy unless truly necessary.  However, if one is truly necessary, it seems likely that the risk is probably not huge.

In the second trimester, it has become routine in the United States to do a more in-depth ultrasound to look for multiple pregnancies, fetal abnormalities, placental problems, as an accompaniment to an amniocentesis, or to confirm gestational age/due dates. Most pregnancies in the US today have one ultrasound at about 16-20 weeks as a matter of course, often to confirm the due date and to look for birth defects, although routine ultrasounds have not been found to improve outcomes (see above). 

In the last trimester, ultrasound may be used to try and determine fetal size (very controversial; see below), fetal position (like  breech), or in conjunction with amniocentesis to determine lung maturity if  early delivery is needed.  It may also be used during a Biophysical Profile (BPP) if there is any concern about the baby's well-being or to be sure the placenta is still functioning well.

Ultrasound for Detecting Ectopic Pregnancy

This is one case where an ultrasound is unquestionably a valuable diagnostic tool.  If a woman has an ectopic pregnancy, then her life is truly in danger.  If she has symptoms that could be caused by an ectopic pregnancy (like bleeding and/or abdominal pain), an ultrasound to discover this or rule this out is clearly justified.  

As always, women may want to opt for a second opinion to be sure the pregnancy is actually ectopic (outside the uterus) before taking any action to end the pregnancy. A second opinion should be done quickly, however, as ectopic pregnancy must be treated quickly in order to preserve a woman's fertility and her life.

Ultrasound for Detecting Miscarriage

If a woman is concerned she may have had a miscarriage, an ultrasound can help her find out whether a miscarriage has occurred.  Most sources report that a baby's heartbeat is usually visible by about 7 weeks by ultrasound, more or less. This (along with quantitative blood tests, etc.) can help determine whether the pregnancy is still viable.  However, it must be cautioned that ultrasounds are more useful for ruling out miscarriage than for knowing for sure whether one has occurred.  

Once the fetal heart is seen beating away, the chances for miscarriage drop dramatically.  Thus, ultrasounds are very valuable for ruling out miscarriage and reassuring the mother that a miscarriage is much less likely now that the heartbeat has been seen.  

But ultrasounds are much less reliable for diagnosing a miscarriage. Even if the heartbeat is not visible yet at 7 weeks, this does NOT necessarily mean that the baby has died.  Sometimes the pregnancy is not as far along as the doctor thought and given time, the baby's heartbeat will show up. Sometimes, the baby's heartbeat just takes a little longer to show up on the screen, especially with a less-powerful machine or less-competent ultrasound techs.  

Goldstein (1992) studied cardiac activity by transvaginal ultrasound scan in early pregnancy and found that "Cardiac function is present in normal embryos before it can be detected on ultrasound."   In the study, absence of cardiac activity in embryos of 4 mm or more was more likely to predict embryonic death, but even when no heartbeat was discernable in embryos of 3 mm or less, there was still a 41% pregnancy continuation rate.  The study concludes, "The lack of cardiac activity in embryos of 3 mm or less is nondiagnostic and may warrant follow-up study in 3-5 days."  

Other factors can also affect the detection of cardiac activity.  Earlier gestational age, coexisting fibroids, obesity, surgical scarring, and a retrograde uterus can also make it harder to 'see' everything adequately.  Therefore, beware making hasty decisions about whether a miscarriage has occurred (or a pregnancy even existed) based on an early ultrasound. 

Christine's Story: I called the doctor's office...with some early first trimester bleeding. I had just tested positive with a home pregnancy test, and after having had two previous miscarriages, was worried about the outcome of my current pregnancy.  Going by my last menstrual [period] or LMP, I should have been six weeks along but because of my long cycles and the fact that we were using natural family planning I knew I was approximately four and a half weeks pregnant...[I went in at about 7 weeks LMP.] At that appointment, I saw Dr. T's nurse practitioner who suggested that due to the bleeding and the discrepancy in dates, an ultrasound done sometime within the next week would be prudent.  I called the radiology department at [the hospital] and they scheduled an ultrasound for the following day.  

I repeatedly informed the ultrasound technician that I was sure there would be no heartbeat as I was not as far along as my dates suggested.  I called Dr. T's office [the next afternoon] looking for a report and was told if something was wrong they would have been notified.  Finally, Dr. T's associate called and informed me that I had a blighted ovum.  They had found an empty gestational sac that did not contain a yolk sac or a fetal dipole.  I made a follow up appointment for 10 days later and left for a few days vacation.  Upon returning from vacation, I did a little research on my own and found that according to when I thought I had ovulated it was possible that they may not have been able to see a yolk sac or fetal dipole even in a healthy pregnancy.  

I discussed this with Dr. T at my follow-up visit.  She was very caring but told me that the results were pretty conclusive.  I asked for a series of hCG beta blood tests to be drawn and was told there was no point.  Dr. T informed me that I had three choices:

  1. We could schedule a D&C for the following day
  2. She could give me a vaginal suppository of a medication that would cause me to spontaneously abort, or
  3. I could wait and let nature do the inevitable.

I told her that I did not want to carry a pregnancy that was not viable for what could be weeks.  However, something inside of me said that ending the pregnancy was not the right decision so I pleaded for a second ultrasound before the D&C just to be sure.  Dr. T replied that if it would make me feel better, then we would get one scheduled.  

I was so nervous the day of the second ultrasound and can't describe the relief and joy I felt the moment the technician told me that she had found a heartbeat.  When Dr. T congratulated me over a phone call that evening, she warned that while the heart rate was in the normal range, it was a little low for that stage in pregnancy (131 bpm).  However, when researching the subject I found that this was actually on the higher side of normal for that stage in pregnancy. Shortly after this...we switched physicians and practices.  We went on to have a successful pregnancy that resulted in the birth of our daughter.  

While Dr. T was a very caring physician, my experience with her practice and [the hospital's] department of radiology left me with the feeling that I should do my best to make sure that this didn't happen to anyone else.  Therefore, I would like to highly encourage Dr. T, the Women's Clinic, and [the hospital] to make it a policy not to suggest terminating a first trimester pregnancy diagnosed as a blighted ovum without first doing a series of hCG beta blood tests and a second ultrasound several days after the first.  

Whether this was a miscommunication between the doctor, her staff, the radiology department, or myself doesn't really matter at this point.  What does matter is that terminating my pregnancy was given as an option to me and I was given no hope that there was the possibility of another outcome.  Fortunately, I was experienced enough with fertility issues to know what to ask for.  I would hate to think of the outcome had I listened to the professionals, and cringe at the thought of what many others that are not as persistent and knowledgeable have lost.  Every day I hold our beautiful little girl in our arms and give thanks for the fact that I went with my heart and insisted on a second opinion.

It is very important to establish securely that a miscarriage really has taken place before having a D&C.  This certainly should be mandatory everywhere, but obviously it is not. Here is another, similar story reported online:

Anonymous Story: I met a mom expecting twins...she experienced extreme heavy bleeding in her early pregnancy and rushed to the ER where they wanted to whisk her in immediately for a D&C.  She demanded on waiting for her regular OB to consult with before making any decisions and also was requesting an ultrasound.  Her regular OB arrived, did the ultrasound, and found TWO sacs and heartbeats.  She must have been expecting triplets but only miscarried one.  Had she followed hospital protocol she would have aborted not 1 but 2 viable fetuses.  

It's important to point out that an ultrasound to detect a miscarriage is not compulsory; many women choose to simply wait to see whether the pregnancy is viable or not.  If the baby is not viable, a miscarriage will show up in time.  Many women prefer the more natural approach, rather than worrying and fixating over whether a heartbeat has shown up yet.

Other women feel they need to know immediately and so prefer doing an ultrasound.  There is nothing wrong with this; it is a reasonable use of technology, if only for the mother's peace of mind.  But it should remain the mother's choice whether or not to use ultrasound to detect fetal viability; women should not be pressured into doing one if they do not want one.  Ultrasounds are not absolutely required if miscarriage is suspected, unless there is a question of ectopic pregnancy.  As always, it's the woman's choice. 

Some women wish to avoid an ultrasound for fetal viability because this usually leads to strong pressure for a D&C, and they do not believe a D&C is necessary for all miscarriages.  Remember that a D&C is not mandatory after a miscarriage.  Many women choose to wait to miscarry naturally.   Although a D&C can minimize some potential complications, it also carries its own risks, including increasing the risk for placental abnormalities in future pregnancies.  This may be particularly true if a woman has had prior cesareans.  (See "Ultrasound for Placenta Previa.")  Each approach has its own advantages and disadvantages, and women should research and choose which approach they prefer from an informed point of view, not because of pressure.

Always remember the weaknesses of ultrasounds in diagnosing miscarriage; they are not 100% accurate.  There have been cases  where ultrasound scans seemed to indicate miscarriage and the provider was pressing for D&C, yet later scans found the baby's heartbeat just fine.   (See the above story, and the "tumor" story below.)  

Always ask for a repeat scan with a more powerful machine and a well-trained doctor before having a D&C.  It may help to wait a week or two between scans to get a more definitive answer, if there are not pressing health concerns.  Discuss the pros and cons of waiting with your doctor.  You may also wish to request quantitative hCG testing as well.  

Ultrasound for detecting miscarriage is a reasonable use of the technology if the mother desires an immediate answer regarding miscarriage, but always remember that results are not 100% reliable.  Be sure further testing is done before making any irrevocable choices.

Ultrasound for Detecting Multiple Pregnancies

Because multiple pregnancies are riskier than singleton pregnancies, and because extra nutrition and close monitoring may be helpful in mitigating these risks, ultrasound for detecting multiple pregnancies is another reasonable use of technology.  

If a woman is at high risk for multiples genetically or because of fertility treatment, an ultrasound scan is reasonable if she wants one.  If the mother is having symptoms of a multiple pregnancy (extreme nausea, extra growth for dates, suspected multiple heartbeats, etc.), then an ultrasound scan is quite sensible, although of course never mandatory.  It should be noted that the RADIUS trial did not find benefits to large scale detection of multiples, but in individual cases, it's possible that ultrasound scanning may be beneficial in cases of multiples with special circumstances.

Scanning for multiple pregnancies can sometimes be a mixed blessing emotionally.  Some multiples die in utero before the end of the first trimester; it is not unusual for one twin to survive and the other to be reabsorbed, for example.  In the past, nearly all of these cases went undiscovered and the mother never knew.  With ultrasound in the first trimester more common now, more women are realizing that they had multiples and lost one, giving them the bittersweet task of mourning one child while celebrating the other.  Some women would prefer to know of a loss such as this, while others would not.  While early detection of twins is probably beneficial overall, the knowledge of the loss of one can be a bittersweet and mixed blessing.  

If there is strong reason to suspect a multiple pregnancy, be sure to request the scan be done with a powerful machine and a highly trained technician or perinatologist.  An accurate report of results will be important, and an ultrasound with a center experienced in scanning for multiples will be quicker, more accurate, and probably result in less overall exposure.  Then counseling can be given about the extra nutrition that will be required for a multiple pregnancy, and a careful plan can be developed for sensible monitoring of the pregnancy.  Extra ultrasounds are generally recommended for women carrying multiples; just how many of these are truly justified depends on the condition of the babies and any other medical co-conditions.  

Ultrasound for Detecting Fetal Abnormalities

Sometimes babies have genetic defects or develop abnormally and experience problems such as Neural Tube Defects (NTDs, such as spina bifida, anencephaly, etc.), heart problems, kidney problems, gastrointestinal problems, hydrocephaly ("water on the brain"), Down Syndrome, Trisomy 18, etc.  Doctors like to test early for these problems, and thus most doctors recommend an ultrasound done somewhere around weeks 16-18.  Although no real benefit has been shown from routine scanning like this, the jury is still out on whether this is a reasonable use of ultrasounds. In some cases it may be quite helpful, while in others it may be neutral or even harmful.   

It is important that parents realize the limits of ultrasound technology.  A "normal" ultrasound is NOT a guarantee of a "normal" child; many conditions are missed on ultrasound ("false negatives").  In addition, sometimes a baby is thought to have a problem but does not actually have it  ("false positives"). At, the authors discuss this problem, stating, "On average, one third to one half of fetal structural birth defects are not detected with ultrasound. Less commonly, ultrasound can sometimes indicate a fetal abnormality when no abnormality is present, causing stress and worry among the parents."  It is important to remember that an ultrasound is not a guarantee of anything.  

Although most ultrasounds tend to be fairly accurate, "false positives" and "false negatives" DO occur and they cause tremendous stress to the parents.  In 1996, Natalie Angier wrote about the "false positive" prenatal diagnosis of club foot with her daughter.  Her article can be read at  Kmom highly recommends reading her story.  

Many women find that such diagnoses create tremendous stress in their lives and change their experiences of pregnancy, and they become especially upset  when they find out later that the "diagnosis" was incorrect.  Here is another story of a "false positive" diagnosis.

False Positive Story: I measured large for dates from the very beginning.  After ruling out gestational diabetes, an ultrasound was done during my fifth month.  My OB/GYN concluded that my dates were off, and I was actually two weeks farther along than my calculations.  This was despite the fact that I knew exactly when my last period was, and the date I conceived.  Doctor knows best, of course.  

At 38 weeks (by my calculations) [40 by the doc's calculations], I was admitted to the hospital to have another ultrasound to determine the size of the baby...The technician estimated the baby to be at 41+ weeks and close to nine pounds.  During the course of the ultrasound the technician got very quiet.  We could tell something was wrong.  She wouldn't tell us, instead saying that we would have to wait and speak to the doctor.  

We went back to my room to wait on my doctor.  I was lying down when he came into the room, along with his partner.  Both of their faces looked very grave.  I started shaking.  My husband was holding my hand.  After what seemed like forever, my doctor spoke.  He said the technician was very certain that she had seen a cleft lip and palate.  Because I have cleft lip/palate, I had very likely passed it on to my baby.  At his words, I quite literally felt my blood turn to ice...I could not speak.  Tears were running down both my husband's face and mine....The doctors told us that they wanted to send me to [a big town] where a better ultrasound could be performed.  If it was determined that the baby indeed had a cleft, [they] would go ahead and induce labor there so that there would be a team of doctors to take care of the baby's needs.  We agreed.  

After thinking about it for a while, I felt very calm.  I knew that if indeed my baby was born with a cleft, then I was the best possible mother for him to have.  I would know how to deal with everything, and I would know how to protect him from the cruelty of the outside world.  I decided that it was a blessing.  He was being sent to a Mommy that could fulfill his needs perfectly.  

We went home and told my family what the doctors had said.  This was very difficult to do.  It was the first time I had ever seen my grandfather cry.  Then he got extremely angry with me for getting pregnant in the first place.  He said he loved me dearly but "people like me" should never get pregnant because of the very situation we were in.  That devastated me and haunted me for years.  

My husband drove me [to the big city hospital] the next morning.  An ultrasound was done.  No cleft was found at all. We were overjoyed.  [After a difficult induction, ending in a terrible cesarean, the baby was finally born.]  The baby was beautiful and perfect...He did not have a cleft.  

In the case of "false positives," follow-up ultrasounds usually clarify that things are fine after all, but at the price of lots of worry from the parents, and lots of extra ultrasound exposure as well.  And most of the time, a "false positive" changes the mother's experience of that pregnancy, even when nothing is ultimately wrong.  That small bit of uncertainty about the diagnosis is unnerving, and researchers have found that these women never view the baby or the pregnancy quite the same afterwards, sometimes even after the baby is born. This is a heavy emotional price to pay, and one many couples fail to consider.  

But sometimes, the baby really does have a "birth defect" of some kind.  Does the foreknowledge of this really help?  What do you do once you know there's a problem?  How do you make those kinds of terrible choices?  Even if you do nothing, what kind of emotional price do couples pay in worry, and in having much of the joy of the rest of their pregnancy taken from them? 

One thing many women don't understand is the underlying assumption behind tests for fetal abnormalities.  Although the ultimate choice is of course up to the woman involved, there is a great deal of strong pressure for women with "abnormal" fetuses to have an abortion.  Doctors usually assume that of course a woman who has a fetus with a birth defect is going to terminate the pregnancy.  Although officially they state that these tests are for information only, unofficially women report subtle but very significant pressure to abort a pregnancy with abnormalities.  

In a newspaper article in 2002, one father spoke of this pressure.  His wife had an ultrasound and amniocentesis at 17 weeks. The ultrasound showed the baby not growing as fast as expected, with less fluid and a larger placenta than expected. The parents had many repeated ultrasounds over the next five weeks, some of which had differing results, both better and worse. The father wrote, 

The doctors assumed that, of course, we would want to abort, as soon as possible.  'We know you can get pregnant easily,' Emma's obstetrician said. 'Why risk an unhappy outcome?'  She urged us to schedule quickly, because it would be difficult to line up a surgeon around the July 4 holiday.  Appalled by the rush, Emma changed doctors, but we never quite escaped the feeling that by holding out, week after week, hoping for better odds, we were being more than a little eccentric.

In the end, after being told that the chances were very high that the baby would be born dead or in a vegetative state and that carrying to term might endanger the mother, the parents opted for abortion, but it broke their hearts. The father wrote, "This is the double-edged scalpel of reproductive science.  The technology that informs you your future baby is mysteriously endangered also makes him real, a boylike creature swimming in utero."  

In fact, most fetuses diagnosed with major birth defects are aborted.  Many doctors view this as appropriate usage of resources, since the parents, the state, and medical insurances no longer then have to care for this child and its lifelong medical bills.  Others do not agree.  What you would decide in this situation would depend on your views of abortion, of course. The decision is yours, and the fact that the decision is yours brings with it new dilemmas and new levels of pain, whatever you choose.  This is an extremely difficult choice, and far beyond the scope of this FAQ to discuss.  Kmom recommends the booklet, "Precious Lives, Painful Choices" for anyone facing a decision like this (see reference list).  

Are there reasons other than abortion for choosing to have an ultrasound to detect fetal abnormalities?  Yes, of course.  Children with some types of Spina Bifida may do better if the child is delivered via cesarean, and if some types of critical heart defects are known ahead of time, doctors can be more prepared to do surgery as soon after birth as possible.  There is more information on this subject at, and also at and Fetal urinary tract blockages may also be able to be treated prenatally, according to some sources.  Other problems may not be readily treatable but doctors will know ahead of time to watch for problems, beginning right at birth.  

However, a problem diagnosed prenatally may sometimes worsen outcome instead of improving it.  The provider's perception of the pregnancy and the baby changes, and some research (see shows that babies diagnosed prenatally were delivered earlier and by more cesareans than babies with the same condition not diagnosed prenatally.  This did not improve outcome, and may have worsened it.  So prenatal diagnosis may be a mixed blessing in some cases.

Sometimes there are also "ambiguous" diagnoses, ones where the radiologists think there might be a problem but can't say for sure, even with further ultrasounds.  These parents are really left in limbo, not knowing what the status of the child is.  With no clear answers, nothing can be done, and parents are left with a ton of anxiety but nothing to do about it.  

Most of the time when there is a problem diagnosed prenatally, there is nothing that can be done differently to improve a baby's prognosis.  You find out there's a problem but that there's little that can be done.  What then?  This is one of the difficult dilemmas presented by prenatal diagnoses.

Some parents prefer to know about any problems ahead of time so that they could grieve these problems sooner rather than later and be more prepared for the baby's situation at birth.  Some research supports the idea that knowing ahead of time can help parents adjust better and be more prepared; some does not.

On the other hand, some parents do not feel that knowing ahead of time was a gift at all.  Barbara Katz Rothman discusses this issue at length in her excellent book, The Tentative Pregnancy.  She talked to many parents who felt like their experiences of pregnancy and birth were tainted by foreknowledge of the baby's problems, and that knowing of even very minor problems took much of the joy and anticipation out of their pregnancies.  The New York Times article mentioned above (the "false positive" for club foot) also found this to be true.  

There is no easy or automatic answer here.  When deciding whether to have an ultrasound to detect fetal abnormalities, think over all these issues beforehand.  Would it be a blessing to know of any problems ahead of time?  What would you do with the knowledge?  What are your beliefs about abortion?  Do you think it would change your experience of pregnancy to know about any problems ahead of time?  How would you handle news of a problem?

It is in the potential detection of fetal abnormalities that ultrasounds, AFP tests, and amnios present the most difficult dilemmas.  No one answer is "right" for every person or situation, and the choices are some of the hardest a person can ever face.  That's why it is very important for couples to discuss the implications of prenatal testing before the process begins, and to understand the implications of their choices.  

Ultrasound for Dating the Pregnancy

Ultrasound can be used to date a pregnancy.  This is very useful if you are unsure of your dates, have extremely irregular or extra-long cycles, or have a surprise pregnancy while not monitoring your cycles.  However, as with other uses, ultrasound for dating can also be a mixed blessing.

To determine the gestational age of the baby, ultrasound techs measure various parts of the baby and compare it to a fetal growth chart.  Early in pregnancy they measure the "crown-rump length" (top of baby's head to the end of its bottom).  Later in pregnancy, they measure the length of a leg bone (femur length) and from one side of the baby's head to the other (biparietal diameter, or BPD). For fetal weight estimates, they add a measurement of the baby's abdominal circumference.  These are the most common formulas used, but sometimes other measurements are done too.

When babies are first conceived, their growth is fairly uniform in the first few weeks, so gestational age dating in the first trimester is fairly accurate.  As babies continue to grow, however, biological variability takes over, and babies begin to grow at different rates.  This means that gestational age dating is less accurate as the pregnancy continues.  In the second trimester, it is fairly accurate, but by the third trimester it is quite inaccurate.  

Most ultrasound resources state that ultrasound for determining gestational age in the first trimester is accurate to within about a week.  Measurements in the second trimester are supposed to be accurate to within about two weeks.  By the third trimester, the accuracy rate has dropped significantly and can be off by as much as three weeks.  

Therefore, if your cycle is very irregular and you need to get the most accurate dating possible, it is best to have an ultrasound as soon as possible after you know you are pregnant.  In this case, the possible risks of exposure to ultrasound in the first trimester are probably outweighed by the pressing need to have an accurate due date.   

Some women, though, don't realize that they are pregnant for a while and may not still be in the first trimester.  Even though the ultrasound dating will be less accurate, it is still worthwhile to have it done in the second trimester so that the woman is not induced prematurely for "post-dates" pregnancy.  Research is clear that ultrasound is very useful at reducing the number of "post-term inductions" in this instance. (For references, see the website at 

However, if you are sure about your dates, ultrasound dating is not very useful.  On occasion, women sure of their pregnancy dates through  fertility charting etc. have been forced to move up their due dates because of ultrasound results.  Often this results in babies being induced or delivered prematurely, which potentially has major health consequences.  

Therefore, be very leery of a doctor moving up your due dates based on ultrasound, especially an ultrasound done later in pregnancy.  Remember that the sizes used to calculate maturity and due dates are based on averages, so if your baby tends to run slightly larger than average (as some large women's babies do) then the baby's estimated age may be off.  

Also, the measurements used to calculate the baby's age are not always easy to do, and small miscalculations can introduce significant errors into the dating  process.  For example, one resource points out that a baby's head is not perfectly spherical but more of an ellipsoid, and so the measurements from one place to another are going to differ slightly.  Even this slight difference in measurement can cause significant differences in datings at times. In addition, Dr. Marjorie Greenfield at cautions:

Due dates by ultrasound are not that exact.  Remember that we are measuring a flat image of a three dimensional fetus, and then estimating how far along the pregnancy is by the millimeters of the leg bone or of a line drawn across the head.  There is a lot of room for being a few millimeters high or low on all of these measurements, not to mention that babies of the same gestational age can be slightly different sizes.

Ultrasounds in the last trimester to predict a baby's age/due date are particularly inaccurate.  Unless there are really extenuating medical circumstances, do NOT let a doctor move up your due date based on a third-trimester ultrasound. There have been big moms who have had their babies delivered prematurely because an ultrasound scan inaccurately estimated the baby's age and the doctor moved up the baby's due date.  Prematurity can cause big problems, so this is not a decision to make lightly. Unless there are very unusual circumstances, ultrasounds in the last trimester should not be used to change due dates.   [See Danielle's Story, below.]

Ultrasound for Detecting Placental Problems

One reason doctors do routine ultrasounds is so that they can detect any cases of low-lying placentas.  In this situation, called "placenta previa," the placenta overlies or is very close to the opening of the cervix, and would prevent the baby from being born safely.  True placenta previa necessitates a cesarean birth.  

However, most cases of placenta previa that are noted on the 16-20 week ultrasound actually resolve before birth.  If you are told that you have a low-lying placenta early in pregnancy, don't panic.  95% of these placentas "move up" and away from the cervix and no cesarean is necessary.  It's good to have these early previas watched, and to be aware to watch for any signs of vaginal bleeding (often a symptom of previa), but 95% of women diagnosed with early previas are worried unnecessarily.

On the other hand, if you have had prior uterine surgery or instrumentation of any kind (i.e., a prior cesarean, an operation to remove fibroids, a D&C), an ultrasound to look carefully for placenta previa DOES make sense.  Although the risk is low, uterine scars and prior instrumentation can cause the placenta to implant improperly in subsequent pregnancies and this is a very serious complication if it happens.

The more uterine surgery and instrumentation you've had, the higher the risk for placental problems, either a low-lying placenta (placenta previa), or a placenta that grows into or through the uterus (placenta accreta or percreta).  Although these can occur in first-time pregnancies, they are most dangerous when associated with prior uterine surgeries. There is a significant danger of massive hemorrhage, hysterectomy, and maternal or fetal death.  

In particular, multiple prior cesareans (especially 2 or more) strongly raise the risk for placental problems. For every cesarean you have, the incidence of placental previa rises sharply in the next pregnancy, from 0.65% after 1 cesarean, 1.8% after 2 cesareans, 3% after 3 cesareans, and 10% after 4 or more cesareans (Clark 1985). If you have had prior uterine procedures, your doctor will probably want an ultrasound to be sure your placenta has implanted safely. 

It is of course your choice whether or not to actually have one; ultrasounds are never absolutely required.  Some midwives will manage a pregnancy after multiple cesareans simply by watching carefully for symptoms of placental problems.  However, the more cesareans you have had, the more beneficial an ultrasound to look for placental problems may be.  As always, though, whether to do one remains the mother's choice.

If an ultrasound seems to indicate a possible problem, remember that many early placental problems---even those in women with prior cesareans----will resolve if given time.  Women with prior cesareans often have anterior placentas (placentas on the front of the uterus instead of the back), and anterior placentas tend to be low and near the scar in the beginning of pregnancy.  Thus an early ultrasound may suggest placenta previa, causing you great worry and requiring multiple scans, yet turn out to be nothing.  

Therefore, don't overreact if an early ultrasound spots the possibility of a low-lying placenta, even if you've had prior uterine surgery. Although these should be watched very carefully, most likely they will resolve in time.  Or choose to delay your ultrasound until after 20-24 weeks or so, when most placentas will have moved away from the scar and you are less likely to get a "false positive" report.  

But if a later ultrasound shows that the placenta is still on or near a uterine scar well into pregnancy, further testing should be used to check the location and degree of implantation of the placenta.  Persistent placenta previa combined with a history of cesareans in particular is strongly suggestive of placenta accreta, and research indicates there should be a high degree of suspicion in this situation.  

Undiscovered placenta accreta is one of the most risky obstetrical situations there is; if there is a placental problem like this, multiple scans will be needed so the full extent of the problem can be known ahead of time. Color Doppler ultrasonic scanning and MRI (Magnetic Resonance Imaging) are generally accepted as the best method for diagnosing placenta accreta.  Most providers will order multiple scans if this is suspected, and obviously the benefits of diagnosis here would outweigh any potential risks of more scanning.

Although most cases of initially low-lying placentas turn out to be normal or only minimally problematic, very careful testing should be done when placenta previa is suspected in a woman with prior cesareans, especially multiple prior cesareans.  Very careful screening with specialized techniques will be needed to establish whether placenta accreta has developed., and obviously this is a justifiable use of the technology.   

Ultrasound During Amniocentesis

There are many reasons why women have an amniocentesis.  Women over 35 are routinely offered amniocentesis, since they are somewhat more at risk for birth defects such as Down Syndrome.   If a woman has a non-reassuring result on other prenatal testing such as the AFP test, doctors often pressure her to have an amnio in order to determine whether the baby has a birth defect.   

An amnio may also be done in the third trimester to determine fetal lung maturity. If a baby needs to come early due to medical complications, doctors must determine whether the baby's lungs are mature enough to deliver.  An amnio can measure the Lecithin/Sphingomyelin ratio (L/S ratio) in the amniotic fluid; a ratio of 2.0 or more is generally thought to indicate a low risk of RDS. However, the presence of the acidic phospholipid phosphatidyglycerol (PG) is considered to be the final marker of fetal lung maturation. There are reports of RDS occurring in women with a mature L/S ratio but absent PG. So if early delivery (before 39 weeks) is deemed necessary, documenting lung maturity with both an L/S ratio and the PG marker is important.  (See GD Treatment Research for references.) Clearly, this is a justifiable use of technology.

Ultrasound is now a routine part of amniocentesis.  It is used so that the doctor can "see" the baby and avoid hitting it with the amnio needle.  Since babies often move in the womb, and especially in response to the mother's stress levels, it is vital that the doctor be able to keep tabs on the baby's whereabouts at all times during an amnio.  Amnios used to be done without ultrasounds, and the complication rates were much higher, including some horrific cases were babies were damaged or even killed accidentally during the amnio.  Rates of such complications have dropped drastically since the inclusion of continuous ultrasound during amniocentesis, and such use is obviously highly beneficial. 

A very complete ultrasound is often done before an amnio in order to examine the baby for signs of problems, in order to confirm the baby's gestational age, to determine the location of the placenta, etc.  Sometimes the results of the ultrasound are enough to determine that there is no need to proceed with the amnio (as when the baby is younger than previously thought, explaining why an AFP test might be low).  But usually, this "level two" ultrasound is just a preliminary to the amniocentesis, and further ultrasound will continue during the actual amnio in order to keep the needle away from the baby and the placenta.  

Obviously, the risks of an amniocentesis make the ultrasound necessary, and is a justifiable use of ultrasound technology.  A better question is whether the amniocentesis is really needed and justifiable.  In some cases it may be, in other cases it may not be.  For more information about the benefits and risks of amniocentesis, click here.  

Ultrasound for Estimating Fetal Weight

Many OBs are fixated on the supposed "dangers" of a big baby (officially known as macrosomia).  Definitions of what constitutes a "big" baby differ, but most research chooses one of the following three cutoffs:  4000 g (just under 9 lbs.),  4500 g (9 lbs. 14 oz.), or 5000 g (about 11 lbs.).  The average size for babies is somewhere around 7 and a half pounds, but babies vary widely around that and are still born just fine.  Although most research considers babies above 4000g to be macrosomic, the American College of Obstetricians and Gynecologists considers 4500g to be a better cutoff for macrosomia.  

Although the risks for shoulder dystocia (baby getting stuck at the shoulders) and birth injuries are increased somewhat among big babies, in actuality MOST big babies are born vaginally without any problems.  But because a few big babies have problems, and because doctors tend to get sued over these types of cases often, they fixate on whether the baby is big or not, in hopes of preventing shoulder dystocia and birth trauma.

This worry leads to one of the most dubious uses of ultrasound----an ultrasound for estimating fetal weight.  This practice is very controversial.  Research clearly shows that ultrasounds for estimating fetal weight are often quite inaccurate, and especially so at the extremes of size (extra-small or extra-large).  Doing ultrasounds for estimating fetal weight is a very questionable policy, but many providers routinely do it anyhow.  

The accuracy of ultrasound for detecting macrosomia seems to run generally from 50% to 65% or so, very low accuracy to be the basis for so much intervention.  For example, Pollack et al. (1992) found that only 64% of the babies estimated to be macrosomic (big) actually were.  Levine et al. (1992) found that HALF of the ultrasound predictions of fetal weight were incorrect. Delpapa and Mueller-Heubach (1991) found that 77% of ultrasound fetal weight predictions exceeded actual birthweight and only 48% were even within 500g (about one pound) of the actual birth weight. Furthermore, 23% were more than 1 pound overestimated, and 50% of the babies predicted to be macrosomic weren't macrosomic at all.  

Notice that predicting macrosomia through estimated fetal weight is as accurate or only slightly more accurate than tossing a coin!  It is not very good science.   Yet doctors routinely continue to order ultrasounds to estimate fetal size, particularly in large women. And these incorrect predictions continue to result in huge amounts of intervention, which have major health implications.

For example, when the baby is predicted to be 'big,' the doctors often  induce labor early in the mistaken belief that this will be more likely to result in vaginal birth and to avoid birth injuries.  Or they strongly pressure women (especially big women) to have an elective cesarean, which brings its own set of substantial risks, both for this pregnancy and any future pregnancy the woman may have.  Unfortunately, research shows that early induction and/or elective cesarean for macrosomia are NOT justified in non-diabetic women, and may be  questionable in some diabetic women too.  

In many cases, induction strongly raises the chance of a cesarean (instead of lowering it), and may increase the risk for birth trauma as well.  Levine (1992) found that inducing for macrosomia increased the cesarean rate from 32% to 53%, and Weeks (1995) found that inducing increased cesarean rates from 30% to 52%.  Leaphart (1997) found that inducing for macrosomia increased the cesarean rate from 17% to 36% in a facility with a generally low cesarean rate, and Combs (1993) found that inducing for macrosomia increased the cesarean rate from 31% to 57%!  

Even when inducing early did not increase the cesarean rate (Gonen 1997), it did not improve fetal outcome or lower the rate of shoulder dystocia.  In fact, in some studies, inducing early actually increased the rate of shoulder dystocia (Combs 1993, Jazayeri 1999, Nesbitt 1998). So although most OBs have been taught that early induction for macrosomia will decrease the chances for cesarean and lower the risks for birth injuries, research actually shows that the opposite is true

Even simply the PREDICTION of macrosomia by estimated fetal weight significantly changes the way the doctor perceives and handles the labor, and strongly increases the rate of induction and/or cesarean.  Weeks (1995) studied the effect of the label of predicted macrosomia.  Those women  who had been predicted to have big babies had a 42% induction rate, and a 52% cesarean rate! Yet the big babies in the study who were NOT predicted to be big had only a 27% induction rate and a 30% cesarean rate.  There was no difference in size between groups; the only difference between groups was the PREDICTION of a big baby.  The authors concluded, " Ultrasonography and labor induction for patients at risk for fetal macrosomia should be discouraged."  

Parry (2000) also found that the mere prediction of macrosomia raised the cesarean rate.  In this study, the cesarean rate for average-sized babies that were predicted to be big was 42%, whereas the cesarean rate for average-sized babies who were predicted to be average was only 24%.  Again, the babies were the same size, but the prediction of macrosomia was enough to nearly double the cesarean rate.  In fact, in this study, just doing the ultrasound to estimate fetal size increased the cesarean rate, which was 20% in the overall population but increased to 40% overall in the women scanned for estimation of fetal size.  

Another study, Levine et al. (1992), analyzed the management of labor based on prediction of macrosomia. Women predicted to have a big baby were diagnosed by their doctors as having more labor abnormalities (30% vs. 19%), had more epidurals (74% vs. 57%), and more cesarean deliveries (53% vs. 32%).  The authors finished by stating, "We observed an association between sonographic estimation of fetal weight at term and the management of labor and delivery. Whether a true cause and effect relationship exists cannot be determined from this study, but, based on our findings, we urge caution in the use of sonographic estimations of fetal weight to guide obstetric decisions concerning labor and delivery."

Obviously, the mere prediction of macrosomia strongly increases the labor induction rate, and in most studies, the cesarean rate.   In most studies, there were no significant differences in shoulder dystocia or birth trauma between groups (or the rate was increased in the intervention group), so the strong interventions did NOT improve outcome at all!  Yet this is still common practice among most OBs, and especially so in large women.

Sacks and Chen, 2000, reviewed the evidence in the medical literature from 1980-1999 and concluded: 

Sonographic estimates are no more accurate than clinical estimates of fetal weight.  Regardless of the method used, the higher the actual birth weight, the less accurate the birth weight prediction…To date, no management algorithm involving selective interventions based on estimates of fetal weight has demonstrated efficacy in reducing the incidence of either shoulder dystocia or brachial plexus injury…For all these reasons, incorporating estimates of fetal weights in the care of nondiabetic pregnant women deemed at risk for macrosomic neonates seems to be unsupported…Available evidence suggests that planned interventions based on estimates of fetal weight do not reduce the incidence of shoulder dystocia and do not decrease adverse outcomes attributable to fetal macrosomia.  [Emphasis Kmom]

Henci Goer, author of The Thinking Woman's Guide to a Better Birth, sums it up when she states, "Studies [on macrosomia] comparing induced women with women allowed to begin labor on their own all show that induced women have more cesareans and equal numbers of shoulder dystocias...Shoulder dystocia isn't very tightly tied to weight, and while it's a dangerous situation, handled properly it rarely results in permanent injury."  

Numerous studies have concluded that the best plan is not to induce labor or to have an elective cesarean, but to prepare and train so that IF a shoulder dystocia occurs, the provider can handle it with the least risk for birth injuries.  It's the handling that often causes the birth injuries, and proper training can reduce that risk significantly.   

Doing an ultrasound to estimate fetal weight near term is a very common practice, one still employed by many OBs, especially with large mothers (see the FAQ on Large Women and Ultrasounds).  However, research clearly shows that this is a very questionable practice.  The accuracy rate is very low, many women are pressured into interventions that do more harm than good, and even the mere PREDICTION of macrosomia alters the way physicians perceive and treat labor.  

A number of studies have questioned the use of ultrasound for estimated fetal weight.  Given its inaccuracy and resulting interventions, this does NOT seem to be a justifiable use of the technology unless co-existing conditions like diabetes are present (even then, some research questions it use).  However, it does remain common despite the research against it.  

Ultrasound for Fetal Position

If there is strong doubt about the baby's position near term, an ultrasound can be very useful for helping to confirm or rule out a malposition.  Most doctors consider a breech position (bottom or feet first) or transverse position (lying sideways) an indication for an elective cesarean, or at least, maneuvers to try and change the baby's position ("external cephalic version," postural changes, Webster's In-Utero Restraint chiropractic technique, etc.).   In that instance, determining the baby's position can guide the provider in important birth and management choices.  

In addition, even relatively minor malpositions like occiput posterior (baby head-down but facing forwards), asyncliticism (head down but head tilted to one side), or compound positions (head down but hand or arm near baby's head) can make a labor harder or raise the risk for a cesarean during labor.  While most OBs shrug off the importance of these positions, research shows that these positions often result in problems.  (See the FAQ on Malpositions on this site.)  Therefore, some OBs and midwives pay close attention to even minor malpositions in order to try and change the baby's position ahead of time or be more watchful for labor difficulties if the malposition persists.  

But is an ultrasound to determine fetal position really necessary most of the time? A baby's position near term can be felt ("palpated") just by a special hands-on technique called "Leopold's Maneuvers."  Although providers SHOULD be able to determine a baby's position near term just by feel, this skill is becoming more and more de-emphasized in clinical training, and providers are relying on high-tech machines instead to "see" for their hands.  

In Kmom's opinion, this is yet another example of important clinical skills being lost because of overreliance on technology.  If your provider cannot tell the baby's position using his/her hands, it raises the question of this provider's real competency.  Too often, OBs concentrate on surgical skills and rare pathologies of birth, but lack competency in basic, hands-on knowledge of normal pregnancy and birth.  If they must rely on technology to do this most basic of tasks, they probably will tend towards over-reliance on technology and intervention during birth itself.  Each mother must ask herself whether this is compatible with their birthing beliefs and wishes.   If you desire a more natural birth, then a provider who must rely on ultrasound to determine fetal position probably is not going to be the best provider for you.   

Some doctors believe that an obese woman's fat makes it impossible to palpate a baby's position reliably, and so will order automatic periodic ultrasounds to monitor fetal position as well as growth.  This is usually an overreaction; a skilled provider can determine a baby's position even on very heavy women most of the time.  In cases of extreme obesity, it may not always be possible to tell a baby's position, but most of the time a skilled provider does not need to resort to extra ultrasounds in women of size.  

However, since many doctors can hardly tell fetal position even in average-sized women, they believe it will be impossible to do so in women of size.  This may be true for them, but this reflects their own lack of skill rather than an automatic rule that heavy women need extra ultrasounds for fetal position assessment.  Most of the time, fat women do NOT need extra ultrasounds for this purpose.  

Occasionally, though, even very skilled providers have difficulty determining a baby's position in women of any size.  Some positions can be tricky to determine with certainty, or an anterior placenta may may fetal landmarks harder to detect. Multiples in particular are difficult to palpate position with, and knowledge of their position is important information to have. Ultrasound can be useful in these difficult cases to give a "window" into the fetal world and is certainly a reasonable use of the technology in these unusual cases.

However, remember that an ultrasound is only a "snapshot" of a baby's position at any one moment.  They often change their positions over time, sometimes very frequently.  Beware making drastic decisions based on such short-term information.  For example, if the baby is breech when an ultrasound is done at 37 weeks, many doctors will probably recommend an elective cesarean at about 39 weeks.  By then, however, the baby may have turned head-down!  

D's Story:  One acquaintance of Kmom was scheduled for a cesarean for a breech baby at almost 40 weeks.  An external version had tried and failed to turn the baby.  Most OBs would tell you that there was almost no chance for this baby to turn head-down at 40 weeks, especially after an external version failed.  However, fortunately D's doctors did order a last-second ultrasound as she was being prepped for the cesarean.  Sure enough, the baby had turned head-down shortly before the surgery was to start!  The cesarean was cancelled and the baby 'allowed' to stay in-utero for another 2 weeks.

You don't want to do a cesarean unnecessarily, so if your baby is breech or transverse and the doctor has scheduled an elective cesarean, INSIST that a last-minute ultrasound be done before proceeding to the O.R.  A cesarean introduces significant risks to both mother and baby, and in particular has implications for any future pregnancies of the mother.  It is not something that should occur on the basis of erroneous information.  Before having a cesarean for fetal malpresentation, have an ultrasound to CONFIRM that position just beforehand.  

Ultrasound for Biophysical Profile

In pregnancies at risk for problems, doctors often like to order a Biophysical Profile (BPP) near term, or when a pregnancy goes significantly  "overdue." A BPP is basically just a prolonged ultrasound that checks on the baby's movements and status in utero.  

A BPP checks fetal movement, fetal body tone, fetal 'breathing' efforts (they are not really breathing, but begin making breath-like movements near term), and amniotic fluid volume.  Each of these is given a numerical score and then they are all totaled up.  Sometimes a non-stress test is also added in.  According to, "A high score (8-10) correlates with a fetus in good condition, while a low score (0-4) often indicates a fetus who might be better off receiving appropriate care outside the uterus.  A score of 6 usually requires a repeat test within 12-24 hours."  

Sometimes a "mini" BPP is done, which combines evaluation for amniotic fluid volume with a non-stress test.  If these are reassuring, many doctors will forego the need for a full BPP, saving time and expense.   Enkin et al., in A Guide to Effective Care in Pregnancy and Childbirth notes: 

There is some evidence that these tests can detect pregnancies in which there is 'something wrong,' but less evidence that their use improves outcome, or can eliminate the additional risk of post-term pregnancy.  The only controlled trial shows no advantages of complex fetal monitoring with computerized cardiotocography, amniotic fluid index, assessment of fetal breathing tone, and gross body movements over simple monitoring with standard cardiotocography and ultrasound measurement using maximum amniotic fluid pool depth.  

Although you don't need to have a full bladder for a BPP, it is wise to be very well hydrated anyhow.  Being dehydrated often shows up as "low amniotic fluid levels," and that can mean early induction. Research shows that many cases of "low amniotic fluid" can be fixed by simply staying better hydrated.  It's a simple way to lower your risk for unnecessary inductions.  

Who needs to have a BPP?  If you have pre-existing diabetes before pregnancy, gestational diabetes (especially insulin-dependent gd), pre-eclampsia, a past stillbirth, a post-dates pregnancy, or other potential problem, doctors like to carefully track the well-being of the baby as it nears birth.  When exactly this is done will depend on the mother's precise situation and the protocols that this particular doctor follows.  It varies widely.  Generally, anywhere from 32-36 weeks is common with co-existing medical conditions (like diabetes); less serious conditions usually start around 38 weeks.   

Does use of the BPP improve fetal outcomes?  This is not clear.  Sometimes a BPP can detect a baby at real risk for problems and in need of immediate delivery, and thus may sometimes save lives.  However, the rate of "false positives" (when the BPP indicates a problem but the baby is actually fine) is high, and the rate of intervention with BPPs is also very high.   Thus while a BPP can potentially save lives, many interventions based on BPPs will not be necessary and may cause more harm than benefit.  Deciding when action is truly necessary and when it is not is a difficult decision, and research is still studying the question of the utility of BPPs in various situations. 

In Kmom's personal non-expert opinion, in truly high-risk pregnancies (i.e. uncontrolled blood pressure, poorly controlled diabetes, past stillbirth and a medical co-condition in this pregnancy), BPPs are a valuable tool and the benefit surely outweighs any possible risks.   BPPs are probably less valuable in detecting low amniotic fluid levels (the error rate is high), and are probably overused in monitoring the pregnancies of women with uncomplicated, well-controlled diet-only gestational diabetes before term.  In other cases, the value of a BPP is more difficult to determine.  

Doctors used to start BPPs and non-stress tests only at 42 weeks for "postdates" pregnancies in the past.  However, their definition of "postdates" has changed markedly, with many doctors calling 41 weeks "postdates" now.  Some doctors even are calling 40 weeks "postdates" and prefer inducing labor at 38-39 weeks instead.  In Kmom's opinion, the changing definition of "postdates" is based on very questionable scientific evidence, so whether this testing or any action because of it is really 'necessary' earlier than 42 weeks is very debatable.  However, it is quite common to start BPPs and non-stress tests at around 41 weeks or even 40 weeks with some doctors.   Whether this is more harmful than beneficial remains to be seen.

While the value of BPPs in postdates pregnancy is debatable, when co-existing medical conditions are present many providers and mothers prefer to err on the side of caution and do the BPP.  "Better safe than sorry" is their view.  Whether this holds up under further scrutiny has yet to be determined but women should not hesitate to do a BPP if their intuition tells them that something may be wrong.  Women often "know" intuitively of problems long before problems become obvious.  On the other hand, don't feel forced into a BPP either.  If in doubt, research your situation and listen to your instincts, whether that means choosing the BPP or declining it.

Ultrasound for Miscellaneous Reasons

Ultrasounds can be used for other, more unusual reasons as well.  It can be used to look for uterine fibroids in the mother and to track their growth and placement during pregnancy.  This is clearly useful if the fibroids may threaten the pregnancy or make vaginal delivery difficult.  Although fibroids do not usually cause significant problems for a pregnancy, they are probably worth monitoring in many cases.

Ultrasound can also be used to look at cervix length if the mother is at risk for premature labor.  If the cervix looks like like it is starting to shorten or change, doctors can be more prepared for the premature labor, use medicine to try and stop it, or use steroids to try and develop the baby's lungs ahead of time.  The efficacy of ultrasound to determine cervical length is still debated at this time, however, so it is not clear whether or not this is a justifiable use of technology.

Ultrasound can also be used to examine the function of the placenta at term, which may be useful in the pregnancies of women at risk for placental insufficiency (i.e. pre-existing diabetics with poor blood sugar control).  How useful and accurate placental function testing is in lower risk women, however, is quite unclear and may be a more dubious use of this testing.

Reasons for Ultrasounds: Summary

Ultrasound use cannot be categorically recommended or condemned. It is clearly greatly beneficial in some cases, and moderately beneficial in others.  However, ultrasound use is not always beneficial or even benign.  In some cases, it may even result in harmful interventions.  Thus, the choice on when to use it and why is a topic still ripe for careful debate.  

Ultrasounds have many varied uses, and no doubt more uses will be found in time.  Whether or not these uses are justified needs careful study before they become routine.  Always question carefully why an ultrasound is being done and what scientific evidence says about its efficacy and possible risks before agreeing to its use.  Then make the judgment that seems right to you in your situation. 


Ultrasound Summary

Ultrasound Safety and Common Use

Ultrasounds can be a very useful tool in certain situations. They are certainly emotionally very rewarding to have!  However, they are greatly overused in US society, raising the costs of healthcare significantly.  This is money that could be spent better elsewhere. Therefore, ultrasound overuse is a matter of important public health debate.

In addition, there have been some questions about the safety of ultrasounds.  Since the strength and specific technology of ultrasounds has increased over time, earlier studies which seemed to find little risk to ultrasounds may not be as applicable anymore.  More research into the safety of newer technologies, into the effects of multiple ultrasounds scans, into the safety of transvaginal ultrasounds, and into the effects of ultrasound on very early pregnancy should be done, using both short-term and very long-term data.  

While it can be emotionally rewarding and very reassuring to have many ultrasounds in a pregnancy, it is probably best to avoid having too many ultrasounds unless medical circumstances truly dictate it. It is Kmom's personal non-expert opinion that one or two ultrasounds is probably reasonably safe in pregnancy, but that unless there are extenuating circumstances, it is probably better to err on the side of caution and limit ultrasounds only to one or possibly two.  

If there are medical complications that justify more ultrasounds, of course this is a reasonable use of the technology.  However, Kmom believes that it is probably best to limit ultrasounds to only those truly medically necessary, and to ask the techs to try and limit the amount of exposure when they do need to be done.  The risk level of having multiple ultrasounds is probably not very large, but if it is not truly necessary, it's always better to err on the side of caution with developing babies. 

Women should also know that an ultrasound is not truly required in pregnancy.  Many women never have a single ultrasound during pregnancy---it's not a requirement by any means!  In fact, ACOG and other organizations do not recommend routine prenatal ultrasound.  If you would prefer not to have an ultrasound, you certainly have that choice.  No one should feel pressured into one automatically.

However, choosing to have an ultrasound is also a reasonable choice.  If you do have an ultrasound there is no need to feel guilty or obsess over risk, as it is probably pretty minimal.  Just use common sense. Use ultrasound only when indicated, and try to minimize exposure as much as you can. Don't overdo just because ultrasounds are so emotionally rewarding to have.  

Like any other test, it's simply a matter of choice whether to do an ultrasound or not, and if so, under what circumstances.  Only you and your provider can weigh those risk/benefit tradeoffs for your specific situation.  But remember also the weaknesses of ultrasound; it is not 100% accurate, and there ARE "false negatives" and "false positives" that occur. If you are given alarming news, always be sure to double-check it, and beware taking any drastic actions based on such results without further corroborating tests.

There are certainly many circumstances in which an ultrasound is a very reasonable use of technology, and at times it may even be life-saving.  We can be very thankful that this new technology is available to us when needed!  But there is a tendency in obstetrics to take technology that greatly benefits a few and require it for virtually all women, without adequate proof of its safety and benefit for such widespread use.  Kmom is not anti-ultrasound, just sounding a caution about indiscriminate overuse of it.   

If you want to find out more about ultrasounds for yourself, be sure to visit the many websites that deal with ultrasound information, including those listed in the references section.  There are many other sites out there as well.  Site URLs change all the time, so you might want to do a search online to get the most updated information. 

Although ultrasounds are generally considered so routine that many medical personnel hardly consider the tradeoff of benefits and risks anymore, they ARE a kind of prenatal testing.  As such, sometimes they bring more uncertainty than reassurance, they often bring further and more invasive interventions, and sometimes they can even result in harm.  Sometimes the benefits of ultrasound may NOT outweigh the possible risks, and sometimes they may.  Weigh each situation on an individual basis, make your choices from a well-informed position, consult your intuition and your baby, and then choose what seems best to you.




The Tentative Pregnancy: How Amniocentesis Changes the Experience of Motherhood.  Barbara Katz Rothman.  New York: W. W. Norton & Company, 1993.  Available from or

An excellent overview of the debate over prenatal testing of all kinds, but especially amnios.  Represents multiple points of view fairly.  Author interviewed a number of genetic counselors, doctors and other health professionals, as well as parents who had been through prenatal testing.  Shares the stories of families who chose testing, who received reassuring and non-reassuring results, and the choices that they made.  Not an easy book to read but certainly one that anyone dealing with prenatal testing should read.

Frye, Anne, CPM.  Understanding Diagnostic Tests in the Childbearing Year.  6th edition.  Portland, Oregon: Labrys Press, 1997.

Superb technical review of ultrasound, how it works, its possible concerns, uses, etc.  Highly technical but extremely thorough.

Precious Lives, Painful Choices: A Prenatal Decision-Making Guide.  Sherokee Ilse.  Maple Plain, Minnesota: Wintergreen Press, 1995.  Available from

An excellent resource for parents who have received non-reassuring test results and now face difficult choices about what to do next.  Written with great compassion and understanding.

Ultrasound? Unsound.  Beverley A. Lawrence Beech and Jean Robinson.  London: Association for Improvements in the Maternity Services.  1994.  Available from

Booklet about ultrasound safety and use from AIMS (Association for Improvements in the Maternity Services) in the United Kingdom.  Explores in detail the past studies which have found possible problems with ultrasound safety, and expresses great concern for the overuse of ultrasounds in society today.  Does not condemn all ultrasound, but rather suggests that each use must be judged on its merits individually.  Although the booklet tends to overemphasize the safety concern issues (in Kmom's opinion), it does raise some very valid questions as well.  Well worth reading, even if you do not agree with everything in it.

A Guide to Effective Care in Pregnancy and Childbirth. Enkin, M. et al. Oxford, England: Oxford University Press.  2000.  Available from Cascade Books,

A medical evidence-based review of obstetric care issues, often in conjunction with the highly recognized Cochrane Pregnancy and Childbirth Database.  Reviewers analyze huge numbers of studies and create a meta-analysis of research data about these issues, and then issue opinions and conclusions based on the evidence available.  An excellent resource.  

Websites About Ultrasound

Websites that contend that ultrasound is probably safe: Websites urging caution about routine ultrasound use:

Newspaper Articles

McCoubrey, Carmel.  "Doctor who warned of prenatal X-rays dies."  New York Times News Service, as seen in The Oregonian, Thursday, July 4, 2002.  

Obituary of Dr. Alice M. Stewart, who died June 23, 2002 in Oxford, England.  Details her struggle to have her research into the safety of prenatal X-rays and other 'low level' radiation exposure taken seriously.  

Keller, Bill.  "Alive in Their Hearts, He Haunts Them Still."  New York Times News Service, as seen in The Oregonian, Sunday, July 7, 2002.

Commentary article about the experience Keller and his wife had with prenatal testing and abortion.  Documents the difficulties, pressures, and moral tangles that such testing brings about.  

Medical Journal Articles

*There are a huge number of journal articles about ultrasound safety, and many websites document these articles extensively.  For space reasons, there is no need to list them all here.  For a very complete listing of such articles, see the websites listed above, especially

Miscellaneous Articles

Newnham JP et al. 
Effects of frequent ultrasound during pregnancy: a randomised controlled trial.  Lancet 1993 Oct 9. 342(8876):887-91.

[from the abstract] "Despite widespread application of ultrasound imaging and Doppler blood flow studies, the effects of their frequent and repeated use in pregnancy have not been evaluated in controlled trials. From 2834 women with single pregnancies at 16-20 weeks gestation, 1415 were selected at random to receive ultrasound imaging and continuous-wave Doppler flow studies at 18, 24, 28, 34, and 38 weeks gestation (the intensive group) and 1419 to receive single ultrasound imaging at 18 weeks (the regular group). Outcome data was obtained from 99% of women who entered the study. The only difference between the two groups was significantly higher intrauterine growth restriction in the intensive group, when expressed both as birthweight < 10th centile (relative risk 1.35; 95% confidence interval 1.09 to 1.67; p = 0.006) and birthweight < 3rd centile (relative risk 1.65; 95% confidence intervals 1.09 to 2.49; p = 0.020). While it is possible that this finding was a chance effect, it is also plausible that frequent exposure to ultrasound may have influenced fetal growth. Repeated prenatal ultrasound imaging and Doppler flow examinations should be restricted to those women to whom the information is likely to be of clinical benefit."

[From Kmom] This study is quite controversial.  Proponents of ultrasound find it to be over-interpreted and the differences in size clinically questionable, while opponents of routine ultrasound contend it has valuable data.  

Ewigman, BG et al.  Effect of Prenatal Ultrasound Screening on Perinatal Outcome. New England Journal of Medicine.  Sept. 16, 1993.  329(12):821-7.  [from abstract]

Famous randomized trial (called RADIUS) involving 15,151 women at low risk for perinatal problems.  Designed to determine whether routine u/s screening decreased the frequency of adverse fetal outcomes.  Women in the screening group had an u/s at 15-22 weeks, and another at 31-35 weeks.  Controls only had u/s if truly medically indicated.  

The rate of adverse perinatal outcome was 5.0% in the u/s screening group, and 4.9% in the control group.  Preterm births, distribution of birth weights were nearly identical between groups.  Furthermore, "Ultrasonic detection of congenital anomalies had no effect on perinatal outcome.  There were no significant differences between the group in perinatal outcome in the subgroups of women with post-date pregnancies, multiple-gestation pregnancies, or infants who were small for gestational age."

The authors conclude, "Screening ultrasonography did not improve perinatal outcome as compared with the selective use of ultrasonography on the basis of clinical judgment."

Goldstein, SR.  Significance of Cardiac Activity on Endovaginal Ultrasound in Very Early Embryos.  Obstetrics and Gynecology.  October 1992.  80(4):670-2.  [from abstract]

Studied the significance of cardiac activity during endovaginal ultrasound in embryos of different sizes in 96 women.  "All embryos that ultimately proved normal showed cardiac activity by the time they were 4 mm in size.  However, absence of detectable cardiac activity in embryos of 3 mm or less was still associated with a 41% continuation rate.  Cardiac activity is present in normal embryos before it can be detected on ultrasound.  There are variations in the type and frequency of ultrasound equipment, maternal anatomical characteristics (obesity, coexisting fibroids, uterine version) , and in the visual acuity of observers.  Nevertheless, we conclude that in our hands, the absence of cardiac activity in embryos measuring 4 mm or more is reliably associated with embryonic death.  In contrast, the lack of cardiac activity in embryos of 3 mm or less is nondiagnostic and may warrant follow-up study in 3-5 days."  

Clark, SL et a.  Placenta Previa/Accreta and Prior Cesarean Section.  Obstet Gynecol.  1985.  66:89-92.

Studied the risks for placental complications as the number of prior cesareans increases.  Found a placenta previa rate of 0.26% in women without prior cesareans, 0.65% after 1 c/s, 1.8% after 2 c/s, 3.0% after 3 c/s, and 10% after 4+ cesareans.  Found a placenta accreta rate of 0.01% in women without prior cesareans, 0.16% after 1 c/s, 0.82% after 2 c/s, 1.1% after 3 c/s, and 6.9% after 4+ cesareans.  

Accuracy and Impact of Estimated Fetal Weight

American College of Obstetricians and Gynecologists.  Clinical Management Guidelines for Obstetrician-Gynecologists: Macrosomia.  Number 22.  November, 2000.

Summary of ACOG's recommended guidelines for clinical practice when macrosomia (big baby) is suspected.  The highlights:

Pollack, RN et al. Macrosomia in Postdates Pregnancies: The Accuracy of Routine Ultrasonographic Screening. American Journal of Obstetrics and Gynecology. July 1992. 167(1):7-11.

519 postdates pregnancies with estimation of fetal weight that occurred within 1 week of delivery were analyzed. Only 56% of fetuses that were actually macrosomic were predicted accurately; only 64% of the fetuses that were estimated to be macrosomic actually were. Notes the dilemma of the doctor presented with a fetus estimated to be macrosomic; they can opt for a trial of labor and risk problems, or they can choose abdominal delivery (c/s) with its attendant morbidity "as long as it is appreciated a priori that in 36% of cases the antenatal diagnosis of macrosomia will not be substantiated" (i.e., one-third of the elective c/s for estimated macrosomia would be unnecessary!!). "At a birth weight of >3750 gm, the Hadlock model (which uses abdominal circumference and femur length) systematically overestimated the birth weight...Routine ultrasonographic screening for macrosomia in postdates pregnancies is associated with a relatively low positive predictive value...Therefore implementation of such screening is of limited use."

Weeks, JW et al. Fetal Macrosomia: Does Antenatal Prediction Affect Delivery Route and Birth Outcome? American Journal of Obstetrics and Gynecology. October 1995. 173(4):1215-1219.

Examines the psychological influence on delivery route and birth outcome of a clinical or ultrasonographic prediction of macrosomia, even in settings where macrosomia is not considered an indication for c/s. 504 patient charts of non-diabetic women delivering babies over 4200g over 5 years were retrospectively examined. Statistical comparisons were made between patients in whom the macrosomia was predicted and those in whom it was not. In those pregnancies where macrosomia was predicted, 42% were induced, and 52% ended with a c/s. In those pregnancies where macrosomia was not predicted, 27% were induced, and 30% ended with a c/s. There were no significant differences in shoulder dystocia or birth trauma, however. "The antenatal prediction of fetal macrosomia is associated with a marked increase in cesarean deliveries without a significant reduction in the incidence of shoulder dystocia or fetal injury. Ultrasonography and labor induction for patients at risk for fetal macrosomia should be discouraged."

Levine, AB et al. Sonographic Diagnosis of the Large for Gestational Age Fetus at Term: Does It Make A Difference? Obstetrics and Gynecology. January 1992. 79(1):55-8.

Retrospective study whose purpose was to determine the accuracy of ultrasound in the diagnosis of the Large-for-Gestational-Age (LGA) fetus and to see whether this influenced obstetric management. 22% of the study group (those with estimated LGA babies) had diabetes, mostly gd. An equal amount of diabetic women were among the controls. Found that the sonographic prediction was incorrect in HALF the cases. Analyzed the management of labor based on LGA prediction: women diagnosed with an LGA fetus were diagnosed by their doctors as having more labor abnormalities (30% vs. 19% controls), had more epidurals (74% vs. 57%), and more cesarean deliveries (53% vs. 32%). 

To determine whether it was the prediction of LGA vs. the actual birth weight causing the differences in management and outcomes, they stratified the study population prediction vs. actual weight. For babies predicted to be LGA but who were, in fact, of average size, the incorrect diagnosis of LGA had a statistically significant effect on both the diagnosis of labor abnormalities and the incidence of elective cesareans, raising the question of how much physician bias and management of suspected macrosomia is to blame for the problems actually associated with macrosomia. "Because this is a retrospective study, only limited conclusions can be drawn. We observed an association between sonographic estimation of fetal weight at term and the management of labor and delivery. Whether a true cause and effect relationship exists cannot be determined from this study, but, based on our findings, we urge caution in the use of sonographic estimations of fetal weight to guide obstetric decisions concerning labor and delivery."

Delpapa, EH and E. Mueller-Heubach. Pregnancy Outcome Following Ultrasound Diagnosis of Macrosomia. Obstetrics and Gynecology. September 1991. 78(3 pt 1):340-43.

Studied 242 nondiabetic women with suspected macrosomic pregnancies (by ultrasound weight estimation). 77% of predictions exceeded actual birthweight; only 48% were even within 500g of the actual birth weight. 23% were more than 500g overestimated. 50% of the babies predicted to be macrosomic weren't. A trial of labor resulted in the the vaginal delivery of 72% of all of these cases. There were 5 cases of shoulder dystocia but no birth trauma. In order to prevent these 5 cases of shoulder dystocia (from which no persistent morbidity occurred), 76 additional c/sections would have had to have been done. "Our study does not support the contention that elective cesarean is justified in those women with fetuses suspected to be macrosomic as a means of preventing persistent infant morbidity. A very large number of unnecessary cesareans would be performed without much preventive effect...early induction does not appear indicated as a means of preventing persistent infant would seem that prevention of morbidity would be best accomplished by proper and immediate management of shoulder dystocia once it occurs...Because shoulder dystocia rarely causes birth trauma, intervention protocols for women with fetuses suspected to be macrosomic include a very large number of patients who are not at risk for infant morbidity. For this reason, intervention--either cesarean delivery or early induction--does not appear to be indicated for fetuses with macrosomia diagnosed by ultrasound."

Parry, S et al.  Ultrasonographic Prediction of Fetal Macrosomia.  Association with Cesarean Delivery.  J Reprod Med.  January 2000.  45(1):17-22.  [from abstract]

Investigated whether incorrect prediction of macrosomia by ultrasound affected the cesarean rate of non-macrosomic babies at two different centers.  Compared 135 babies predicted to be macrosomic (>4000g) with 129 babies predicted to be between 3000-4000g.   Those babies of normal size INCORRECTLY diagnosed as macrosomic had a 42.3% cesarean rate, compared to a 24.3% cesarean rate among babies correctly predicted to be average-sized.  The incorrect prediction of macrosomia almost DOUBLED the cesarean rate, even when the babies were basically the same size.  "Even in nonmacrosomic neonates the antenatal ultrasonographic diagnosis of suspected macrosomia is associated with a significant increase in cesarean delivery rates."

Sacks, DA and Chen, W.  Estimating Fetal Weight in the Management of Macrosomia.  Obstetrics and Gynecological Survey.  April 2000.  55(4):229-39. 

Authors did a medical literature review from 1980-1999, analyzing whether estimates of fetal macrosomia decrease adverse perinatal outcomes.  Notes that while shoulder dystocia and birth injuries occur more often in macrosomic babies, a high percentage occur in average-sized babies as well, and “persistence of impairment is extremely rare.”  They conclude that, “Available evidence suggests that planned interventions based on estimates of fetal weight do not reduce the incidence of shoulder dystocia and do not decrease adverse outcomes attributable to fetal macrosomia.”  

Alsulyman, OM et al. The Accuracy of Intrapartum Ultrasonographic Fetal Weight Estimation in Diabetic Pregnancies. American Journal of Obstetrics and Gynecology. September 1997. 177(3):503-6.

Compared the accuracy of ultrasonographic fetal weight estimation in pregnant diabetic women with that of matched non-diabetic controls. Significantly greater error in size prediction was observed in babies above 4500g. "When matched for maternal body mass and birth weight, the accuracy of ultrasonographic fetal weight estimation was similar among diabetic and nondiabetic women. Birth weights > or = 4500 g rather than maternal diabetes seem to be associated with less accurate ultrasonographic fetal weight estimates."

Johnstone, FD et al. Clinical and Ultrasound Prediction of Macrosomia in Diabetic Pregnancy. Br J Obstet Gynaecol. August 1996. 103(8):747-754.

Examined serial ultrasounds in diabetic pregnancies (most type I and II, with a few gd pregnancies too) to determine prediction power. "All measurements are poor predictors of eventual standardised birthweight...There is no difference in the prediction power for macrosomia between clinical and ultrasound measurements. Even regular serial scanning and clinical examination will not always diagnose the macrosomic fetus in diabetic pregnancy. In our hands, clinical examination is as predictive as ultrasound measurements. Ultrasound does add to clinical prediction power but only to a small extent. Ultrasound should be used in a selective way, as defined by clinical findings, and with recognition and understanding of the errors and biases involved."

Cohen, B et al. Sonographic Prediction of Shoulder Dystocia in Infants of Diabetic Mothers. Obstetrics and Gynecology. July 1996. 88(1):10-13.

Predicting shoulder dystocia is very tricky, even in macrosomic infants of diabetic mothers. This study retrospectively looks at a specific technique of ultrasound examination (comparing the difference between the abdominal diameter and biparietal diameter, or "AD-BPD difference") to see if it is better at predicting shoulder dystocia in this group, since these infants sometimes experience preferential growth in the truncal area as opposed to the head. Eligibility requirements included diabetic pregnancy, ultrasound with the above measurements within 2 weeks of delivery, estimated fetal weight of 3800-4200g, and vaginal delivery. Found 31 patients who fit this criteria; 6 had shoulder dystocia (rate of 19%). Rate of injury and conditions of laboring (position, stirrups, etc.) not noted. The mean AD-BPD difference for the shoulder dystocia group was 3.1, whereas the mean for the non-shoulder dystocia group was 2.6. Therefore, the trunks of those babies who experienced shoulder dystocia were asymmetrically larger. Shoulder dystocia occurred in 6 of 20 patients (30%) with a AD-BPD difference of at least 2.6, but not in any of the 11 patients where it was <2.6. Therefore the authors propose using this test and this cutoff to identify "those fetuses at high risk for birth injury." This sounds promising, but it's also important to note that if 2.6 were used as the cutoff for doing an elective c-section, only 30% of those c-sections would have been necessary to prevent shoulder dystocia; 70% would have been unnecessary! And not all of those infants with shoulder dystocia have injuries; how many more c-sections would have been unnecessary by the criteria of actually preventing injury?

Induction of Labor for Macrosomia

Goer, Henci. The Thinking Woman's Guide to a Better Birth. New York: Berkeley Publishing Group (Perigee Book). 1999.

Outstanding review of childbirth issues, especially induction. "Studies [on macrosomia] comparing induced women with women allowed to begin labor on their own all show that induced women have more cesareans and equal numbers of shoulder dystocias...shoulder dystocia isn't very tightly tied to weight, and while it's a dangerous situation, handled properly it rarely results in permanent injury."

Combs, CA et al. Elective Induction versus Spontaneous Labor After Sonographic Diagnosis of Fetal Macrosomia. Obstetrics and Gynecology. April 1993. 81(4):492-496.

Compared elective induction of labor with spontaneous labor for effect on c-section rate and shoulder dystocia rate in 159 non-diabetic cases where macrosomia was predicted by ultrasound. Found that c/s rate was doubled in the induction group and the shoulder dystocia rate was higher too, though not by a great deal. The induced group had a c/s rate of *57%*! The spontaneous labor group had a c/s rate of 31%, still very high but certainly much less than the induced group! After correcting for potential confounders, elective induction was associated with a 2.7x risk of c/s. "Because elective induction of labor increased the cesarean rate and did not prevent shoulder dystocia, we conclude that mothers with macrosomia fetuses can safely be managed expectantly unless there is a medical indication for induction."

Leaphart, WL, et al. Labor Induction with a Prenatal Diagnosis of Fetal Macrosomia. J Maternal Fetal Med. March-April 1997. 6(2):99-102.

Studied 53 non-diabetic patients who underwent induction for fetal macrosomia, and compared their c-section rate to the same number of women delivering a child of same or greater weight entering labor spontaneously. Theorized that since their institution has a low c/s rate, their induction c/s rate would not be different from their spontaneous labor c/s rate in women with babies of similar size. However, they were surprised to learn that the c/s rate in the induction group was double the rate in the spontaneous labor group (36% vs. 17%). "An increased risk of cesarean delivery was observed in subjects undergoing induction for the indication of fetal macrosomia. These data support a plan of expectant management when fetal macrosomia is suspected."

Gonen O, et al. Induction of Labor versus Expectant Management in Macrosomia: A Randomized Study. Obstetrics and Gynecology. June 1997. 89(6):913-917.

The aim of this study was to determine whether or not induction of labor in cases of macrosomia at term improves maternal and neonatal outcome, as many have proposed. 273 non-diabetic patients at term with an estimated fetal weight of 4000-4500g were randomized into an induction of labor group and an expectant management group. The rates of c/s delivery and neonatal outcome were not significantly different between groups. "In this prospective, randomized study, induction of labor for suspected macrosomia at term did not decrease the rate of cesarean delivery or reduce neonatal morbidity. Ultrasonic estimation of fetal weight between 4000 and 4500 g should not be considered an indication for induction of labor."

Jazayeri, A et al.  Macrosomia Prediction Using Ultrasound Fetal Abdominal Circumference of 35 Centimeters or More.  Obstetrics and Gynecology, April 1999.  93(4):523-6.

Compared macrosomic (>4000g) babies with recent ultrasound exams with macrosomic babies with average-wt. babies with recent ultrasounds to see if abdominal circumference accurately predicted macrosomic infants at risk for shoulder dystocia. Found that abdominal circumference measurements identified >90% of macrosomic infants at risk for shoulder dystocia BUT found that induction of labor in macrosomic patients TRIPLED the risk for shoulder dystocia.   Spontaneous or augmented labor patients had a shoulder dystocia rate of 8% vs. a 22% rate among those induced for macrosomia.   

Nesbitt, TS et al. Shoulder Dystocia and Associated Risk Factors with Macrosomic Infants Born in California. American Journal of Obstetrics and Gynecology. August 1998. 179(2):476-80.

Examined the one-year incidence of shoulder dystocia and associated risk factors in California. Macrosomia was defined lower than usual as >3500 g (usual definition is >4000g, often higher). Found an increased risk of shoulder dystocia associated with diabetes (1.7x risk), assisted delivery--i.e. vacuum or forceps assistance (1.9x risk), and induction of labor (1.3x risk). Of special note here is that the use of forceps/vacuum increased the risk of shoulder dystocia in non-diabetic births by 35-45%. Shoulder dystocia was also strongly increased in diabetic births 'assisted' by vacuum or forceps. The highest risk for shoulder dystocia appears to be in induced diabetic labors with infants over 3500g where the OB uses vacuum or forceps to 'help' things along. Whether this is an argument for elective c/section in these cases or an argument against excessive interventions like routine induction and forceps use from the OB is debatable. Of special note is their statement that "The inaccuracy of estimating fetal weight is a severe limitation in attempting to establish guidelines designed to prevent shoulder dystocia."  

Bruner, JP et al.  All-Fours Maneuver for Reducing Shoulder Dystocia During Labor.  Journal of Reproductive Medicine.  May 1998.  43(5):439-43.

Famous home-birth midwife Ina Mae Gaskin was taught by Central American midwives that putting a woman on all-fours often resolved any cases of shoulder dystocia quickly and easily.  This technique, rarely used in obstetrics but more often in midwifery, has become known as the “Gaskin Maneuver.”  This study examined 82 cases of shoulder dystocia managed with this technique.  83% of the women delivered without the need for any additional shoulder dystocia techniques.  There were no deaths, and only minor problems in 4 deliveries (all in babies over 4500g).  The problems were 1 postpartum maternal hemorrhage (no transfusion needed), one humerus fracture, and two cases of initially low Apgar scores.  Most notably, there were no infant deaths, no Erb’s palsy, no seizures, no fractured clavicles, no newborn hemorrhages or cerebral palsy, etc.   60% of the mothers delivered over an intact perineum (and of those with episiotomies or tears, all were first or second-degree), with no vaginal, cervical, or uterine lacerations.  None of the mothers needed anesthesia, and no deliveries were assisted by forceps or vacuum extractor.  The Gaskin maneuver worked on average within 2-3 minutes, was very non-invasive for the mother, and rarely needed any other maneuvers.  The authors (including two M.D.s) conclude that, “The all-fours maneuver appears to be a rapid, safe and effective technique for reducing shoulder dystocia in laboring women.”  

Gross, SJ et al.  Shoulder Dystocia: Predictors and Outcome.  A Five-Year Review.  Am J Obstet Gynecol.  February 1987.  156(2):334-6. [from abstract]

Records the incidence of  shoulder dystocia from 1980-85 at Toronto General Hospital.  91 cases were coded as shoulder dystocia, but only 24 cases qualified as "true shoulder dystocia" (an incidence of 0.23%).   True shoulder dystocia was associated with neonatal morbidity like respiratory arrest or birth injuries (42%), a very high rate.  The study found that fundal pressure alone was very strongly associated with "orthopedic and neurologic damage" and had a 77% complication rate.  The authors promote delivery of the posterior shoulder and the corkscrew maneuver instead, as these were more associated with good fetal outcome.  


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