Ultrasounds in Women of Size
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 misc.kids.info on the Internet.
This FAQ covers ultrasound information and issues specific to women of size. Big moms are STRONGLY urged to read the FAQ on Ultrasound Safety and Accuracy BEFORE reading this FAQ, so that they can better understand the benefits and risks of ultrasounds before reading about their implications in women of size. Kmom can't emphasize the importance of reading BOTH FAQs strongly enough! [However, please note that some duplication between FAQs was necessary in certain spots.]
"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.
For more complete information about how ultrasound works and different types of ultrasounds, be sure to read the FAQ on Ultrasound Safety and Accuracy on this website. Kmom highly recommends reading this other FAQ before reading this one.
Methods for Doing Ultrasounds
The two most commonly-used methods for doing ultrasounds are:
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 www.ob-ultrasound.com.
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.' Thats 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 level.
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 women with retrograde uteri.
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.
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.
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 (see below) 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
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 ultrasound fetascopes) are the little machines that most providers use every month to listen for fetal heart rates. 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. 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 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.
Concerns of Larger Women
Many large women have a lot of fears surrounding ultrasounds. Although ultrasounds can be a bit more difficult in larger women, the vast majority of the time ultrasounds turn out just fine in women of size.
The following are some of the most common concerns of women of size when getting an ultrasound. Remember, of course, that while some big moms have experienced these problems, most big moms have not. Remember, 'your mileage may vary' from the following experiences. Just because one big mom has experienced this doesn't mean you will! But as always, be ready to be assertive about your care and demand respectful treatment.
"They Won't Be Able to See Everything"
Many larger women express fears that their providers "won't be able to see through all that fat" during an abdominal ultrasound. They may feel embarrassed to have someone touching that soft, squishy part of them, the source of so much derision for some people. They may be afraid that their fat will somehow make the ultrasound impossible.
In reality, however, these fears are largely unfounded. During early pregnancy, nearly all women get transvaginal ultrasounds anyhow, even skinny women. As pregnancy progresses, average-sized women may be able to use abdominal ultrasounds earlier than larger women, but within a few weeks even the largest woman is able to have an abdominal ultrasound.
Will they be able to see everything? It is harder to do an ultrasound on a big person, and the bigger the tummy, the more difficult it can be to see everything they want. However, other factors are can be more important than the size of the mother. These can include:
Don't assume that any problem must be because of your fat. Often the baby is not in the best position for optimal viewing, the u/s tech is not very skilled, or the machine is not powerful enough to get good resolution of what they are looking for. Fat can make it harder to get the best view, but there are certainly many other factors that are just as important.
In most cases, ultrasound technicians are able to "see" everything they need to, even in very large women. However, there are times when it may be difficult to see very subtle details of the baby, especially if the baby's position is less than optimal. One of the most common problems with ultrasounds in women of size is difficulty in seeing the baby's heart fully to be sure it is well-formed and healthy, or difficulty in seeing the fetal spine clearly. Another common difficulty is seeing the mother's ovaries closely enough to make sure that there are no tumors or other problems.
If the sonographers have significant concerns about not being able to see something clearly, they may request that you come back for a second ultrasound a little bit later. Chances are that everything is fine; they may just want to reassure themselves that all is well. It is your choice whether you want to return for a second ultrasound or not; sometimes technicians overreact to a woman's size and order extra testing unnecessarily. Other times, a second ultrasound may clearly be indicated. Use your own judgment on what is the best choice in your situation.
If they are having trouble "seeing" something in your ultrasound, there ARE techniques that can help resolve the imagery better. See below for further suggestions.
"The Ultrasound Won't Be As Accurate Because of My Size"
As noted above, an ultrasound can be harder to do in women of size, and visualization of the soft parts of the baby may make it harder to diagnose problems in the fetal heart, spine, or occasionally the urinary system. Because of this, there is some degree of uncertainty that is inherent to any ultrasound done in a woman of very large size. However, most of the time, an ultrasound done by a technician who specializes in prenatal ultrasound and who is working with a very powerful machine is able to see everything needed.
Ultrasound is very commonly used in women of size to estimate fetal weight (although the value of this procedure is highly questionable, see below). One important question is whether a woman's larger size makes it more difficult to accurately predict her baby's size. Since a woman's size can make it harder to fully visualize the fetus' internal organs, does it make estimated fetal sizes less accurate in big women?
The answer to this is no. Because estimated fetal size is based on measurements of bones (the head, the femur) plus the abdominal circumference, there is less interference with imaging quality. In other words, when ultrasound is used to check on fetal soft tissues, the maternal tissues in between (layers of fat) can interfere somewhat with image quality. However, when ultrasound is used to check on fetal hard tissues (like bones), the image quality is much clearer and is not affected by maternal fatness.
Some doctors will tell women that they cannot accurately predict fetal size in larger women because girth makes it harder to do an accurate ultrasound. The unspoken interpretation in their minds may be that all fat women have huge babies, and any ultrasound that shows an average-sized baby may well be off because the woman's size makes it too hard to get accurate readings. Even when an ultrasound predicts an average-sized baby, some doctors will discount the results and intervene anyhow, convinced the woman is carrying a big baby.
However, research shows that because it is based mostly on measurements of hard tissues or easily seen landmarks like abdominal circumference, estimated fetal size is just as accurate in women of size as in women of average size (Field 1995). Unfortunately, this doesn't say much, since ultrasound estimates of fetal size are only slightly more accurate than the toss of a coin, especially at extremes of size. They are not very reliable for predicting a big baby. But they are not less accurate in women of size, no matter what some doctors believe.
"I Will Get Treated Badly Because of My Size"
Many large women fear that the technicians will make insensitive remarks or or treat them badly because of their size. Although sometimes large women have experienced this (as can be seen by a few of the ultrasound stories below), rest assured that most large women do not experience hassles or derogative remarks during their ultrasounds. If they do, these women should of course speak up and make clear that they will not tolerate this kind of treatment!
If any technician or health-care worker is EVER disrespectful or callous about your size, you should protest immediately, communicate your concerns, and demand better treatment. Discontinue the procedure if the situation does not improve immediately, and report the problem to their supervisors and request a different ultrasound tech. Although many large women find it difficult to be assertive like this, this is the perfect opportunity to start standing up for yourself! Health care workers have been getting away with poor treatment of fat people for a long time, and it's time that this practice stopped. If you find it difficult to do for yourself, do it for your baby!
ALL WOMEN DESERVE RESPECTFUL, CARING HEALTH CARE, REGARDLESS OF SIZE. No health care worker should ever get away with anything less than respectful treatment, especially since they will continue to treat all large woman badly until someone calls them on it. Be assertive about your treatment, both for your own sake and for the sake of all the fat women who will follow after you, and for the sake of the new generation of children that will follow after us. Draw the line and REFUSE to accept mistreatment.
"The Technician Says My Ultrasound May Be Incomplete Because of My Size"
As noted above, it's true that being large can make ultrasounds a bit trickier to do or to interpret. However, this is no reason for disrespectful treatment or callousness. If the technician points out gently that interpreting the ultrasound might be harder, this is a reasonable statement. This is simply important information being passed on to you, not necessarily a judgment.
However, if they berate you for your size, are hostile or extra rough with you, or tell you that there will be 'no way to know for sure whether your baby is deformed because of all the fat in the way,' that is something entirely different! This is judgmental and abusive and should never be tolerated. It's all in the attitude and how they act towards you.
Most technicians never say a word about abdominal adiposity (fat) making it harder to see everything completely. Others may list the exam as being somewhat incomplete on the official report, since it's possible for adiposity to interfere with images. Usually, this is just for liability purposes, to cover themselves in case something undiscovered comes up later. It doesn't necessarily mean they are trying to be cruel; they may simply have been taught to always mention this in a report to cover themselves "just in case."
However, sometimes techs use this as a way to be cruel. It is true that it can be harder to do an ultrasound in a woman of size, but how they discuss it and how they act about it is just as important as what they say. Cruel or rude treatment should never be tolerated, even if the points they express have some basis in reality. If they have concerns, they can discuss it with you in an objective and non-judgmental way.
But simply mentioning that size may make the ultrasound harder to do or perhaps less complete doesn't mean they are being size-phobic. Most of the time, it is just a formality that regularly gets added to the u/s report, a "CYA" for liability purposes. On the other hand, if the technician is rude or condescending about it, that should not be tolerated either. It's all about how they say it and how they treat you.
If you encounter a situation like this, acknowledge to them that you understand that it can be harder to do a complete ultrasound on a woman of size, but that there is no reason to be rude or disrespectful about that fact, and that you will report them to their supervisor if they continue to use a rude approach with you. Sometimes medical personnel are not aware of their biases and will respond if you express your concerns. Other times they get defensive or more hostile, but will back down if reported to their supervisors. Regardless of how they respond, NEVER tolerate disrespectful or biased treatment.
"They Will Press Too Hard"
Sometimes doctors and technicians can be rougher in an ultrasound with a larger woman because they feel that they must press down extremely hard in order to compensate for a bigger tummy. This is one of the most common complaints of larger women after an ultrasound; it can be really uncomfortable if they do this!
However, personal technique has a lot to do with comfort level. Many larger women who have had multiple ultrasounds report that it hurts more with some providers than with others. Why should it hurt with some providers and not with others? Perhaps these providers are assuming unnecessarily that extremely firm pressure will be needed. The best approach is to acknowledge tactfully that adiposity can cause problems, but that you'd prefer it if they started more gently at first, and then increase pressure only if and when needed. Most technicians, if approached nicely, will agree to this.
It's also important to note that pushing too hard can sometimes cause distortions in what the technicians 'see.' Some large women have had the experience of the technician pushing extremely hard, then being told that their baby had problems. If you are told that your baby has deformities or other problems based on an ultrasound scan and they seemed to be pushing pretty hard, ask for the scan to be repeated with a transvaginal scan or by a perinatologist (who tends to have the most advanced equipment). Although it is uncommon for images to be distorted from too-strong pressure, it has happened, and should be ruled out as a cause before making a final diagnosis.
Jessica's Story (paraphrased): I had an ultrasound at 18 weeks. I was told my weight made it impossible to scan the baby, and they saw encephaly [Kmom note: Hydrocephaly?] on the scan. They told me he was going to have a grossly misshapen head and that I'd need a c-section. They sent me to a high-risk OB. He saw the scan and said, "Wait a minute, you're pushing too hard! Do a vaginal!" They did the vaginal and there was our rascal, safe and sound, the right size, and no deformity. I was sore for a week after the abdominal scan, the transducer hurt so bad.
Ask for a transvaginal if they start to push too hard, or ask your OB to send you to a perinatologist for a better scan. What happens when they push too hard is they distort and add artifact to what they can't see, and the baby looks deformed to their measurements.
Again, a technician pressing too hard is one of the more common problems experienced by women of size during an ultrasound. They often have been told that this is 'necessary' in women of size and may simply be going by what they were taught. Although more firm pressure may be needed on women of size, you should NOT have to endure pain during an ultrasound.
If you experience this problem, let the tech know that he/she is hurting you. Let them know that you realize that doing an ultrasound on a heavy person can be more difficult, but suggest that they try more gently at first and only increase pressure if needed. Alternatively, suggest that they try the ultrasound again after you lift your 'apron,' try imaging from the side if needed, do a transvaginal scan instead, or put the transducer inside the belly button instead. If a clear image is still a problem, you can try again in a few weeks when the baby may be bigger, or in a better position. Ask to have the ultrasound on the most powerful ultrasound machine possible, and done by the most skilled person available (a perinatologist, if something serious is suspected). This is enough to solve the problem in nearly all cases.
The other option is simply to forego the ultrasound completely. It is certainly not a requirement in pregnancy to have one (or for it to be 100% complete) and many women simply choose to omit any more ultrasounds rather than go through the hassle and worry of getting multiple ultrasounds. In most cases, everything turns out just fine anyhow; most cases of 'possible problems' turn out to be nothing.
Ask yourself if a definitive answer is important to you and whether it would change management of your pregnancy at all. If not, then perhaps a further ultrasound is not worth the hassle. On the other hand, if you need it for your peace of mind, don't hesitate to pursue further imaging, either. Do what seems best in your circumstances.
Techniques To Help Improve Ultrasound Results in Women of Size
As noted, it can be harder to "see" everything clearly when doing an ultrasound in a woman of size. In particular, the most common problems seem to be visualizing the baby's heart and/or spine thoroughly, as well as being able to "see" whether the mother's ovaries are healthy and normal.
As noted above, some women may choose to simply forego another ultrasound for further clarification of these issues. Chances are very good that the baby is fine and that all is well. Absolutely definitive answers are an illusion with ultrasound anyhow, and some women are less caught up in the "need to know" as much as possible ahead of time.
On the other hand, some women have a strong need to for as much information as possible. For these women, certain techniques may help clarify ultrasound images. For example, often just coming back for another ultrasound in a few weeks is enough to "see" everything more clearly. The baby is older, the uterus has lifted up out of the pelvis a bit more, and the baby may be in a better position the second time. These factors can be very important. Requesting that the follow-up ultrasound be done on a more powerful machine in a center that specializes in prenatal ultrasound may also improve results as well.
There are also several other refinements that can be done if the technician has difficulty resolving the images adequately. First, if you have a large 'apron' (saggy belly), they may ask you to pull it up a bit and hold it back, especially if you are around the end of the first trimester/beginning of the second trimester. This is when getting abdominal images is tougher anyhow and the uterus is not very big or high up in the pelvis yet, so pulling back the belly a little (if necessary) might make sense in this instance. Don't be embarrassed. Your body is simply your body, and it's not that uncommon in diagnostic tests to have to pull and push things this way and that a bit. Be matter-of-fact about it and just do it. It really can help.
Turning the woman on her side and putting the transducer on her side may also help clarify the images, especially if the baby's position is less than optimal, or if there are multiple babies inside. One woman found this to be helpful in her twin pregnancy:
"When I had ultrasounds during my twin pregnancy I was about 300 lbs. and sometimes when they couldn't see just right, they would have me lay on my side and try from the side! Technicians were always polite and accommodating!"
If this is unable to resolve the image, they may need to go to a trans-vaginal ultrasound instead, but remember that this is very common around the early part of the second trimester and nothing to be embarrassed about. There is often a "window" of time early in the second trimester when it is debatable whether to use abdominal or vaginal ultrasound in women of any size, but especially in women of size. It becomes a judgment call on the part of the u/s tech, and sometimes they make the wrong call. If they need to switch modes, then it's no big deal. Don't feel embarrassed.
Another technique they can use to clarify images later in pregnancy is to put the transducer (usually a vaginal transducer) inside your belly button. This is uncommon and probably a little uncomfortable, but if there is an image that needs clarification, some research has reported success with this, especially with visualizing the fetal heart.
Rosenberg (1995) reported on their experience using transvaginal probes in the belly buttons of obese women to help improve ultrasound resolution. 19 of the 25 cases involved incomplete imaging of the fetal heart. Techs filled the women's belly buttons with ultrasound transmission gel, and then a transvaginal probe was inserted into the belly button. This improved image resolution and resulted in satisfactory heart images in 18 of the 19 women with incomplete fetal cardiac reports. All told, 24 of the 25 heavy women (96%) were able to have a 'complete fetal survey' using this technique.
Although it doesn't sound fun, transumbilical ultrasound is usually not traumatic. Like the other types of ultrasound, it probably involves a bit of pressure and pushing, and may be a bit uncomfortable at times. As with the abdominal ultrasound, ask the technician to start more gently and then increase the pressure only if needed.
Sometimes it is harder to do ultrasounds in larger women, but there are techniques that can help. Although techniques such as vaginal ultrasound, laying a woman on her side, pulling up the apron, or umbilical ultrasounds can be a bit more uncomfortable emotionally and physically, don't be embarrassed if this is necessary. It's simply a matter of finding the right technique for the job. Most mothers are okay with these things if it means being able to resolve a question of their baby's health. But also remember that MOST large women do not need these extra techniques. When they do, it may simply be an indication of the power of the machine used, the skill of the technician, the age of the baby, or the baby's position. It's not always about size!
Rest assured that most large women have an unremarkable experience with ultrasounds. On occasion, there may be difficulties with not being able to see everything as thoroughly as they'd like because of a woman's size, but it's reassuring to know that even then, there are further techniques that can be tried that will result in a satisfactory ultrasound image in the vast majority of large women
The Debate Over Extra Ultrasounds in Women of Size
Many providers order extra ultrasounds for women of size, as noted above. Most of these are not justified, although of course each situation must be judged on its own merit. But in general, in a healthy big mom without added medical conditions (like hypertension, pre-eclampsia, or diabetes), extra ultrasounds are usually not necessary simply because of size.
The most common reasons given for extra ultrasounds in big women include:
Checking for Fetal Abnormalities
Because larger women are at a somewhat higher risk for NTDs and defects such as fetal heart problems, they are sometimes strongly pressured to have extensive, multiple ultrasounds. However, it should be pointed out that while heavy mothers do have an increased risk for some birth defects, this risk is still not very high, and that MOST obese women have normal pregnancies and healthy babies. Chances are still very good that everything is fine with the baby. Detailed scans looking intensively for birth defects are not a compulsory requirement for big women.
Although in-depth research is still scarce on this subject, some heavy women may be at more risk for birth defects than others, and this may alter their decision-making process on extra ultrasounds. For example, some research indicates that women who are both obese and diabetic are at a significantly increased risk for birth defects compared to women who are simply obese or simply diabetic. Women who know they are diabetic, are borderline diabetic, and/or have a strong family history of diabetes might therefore consider more detailed ultrasounds. This is by no means required, and most scans will still turn out negative, but it is a choice that is available.
Limited research also suggests that women who have lost quite a bit of weight during pregnancy may also be at increased risk for NTDs. Since dieting often depletes the body of B vitamins, it seems logical that women who crash-dieted or lost a lot of weight prior to or during early pregnancy might be at risk. (References for these studies are in the FAQ on Large Moms and Neural Tube Defects.) These women may also want extra scans if they are concerned.
In addition, women who had a surprise pregnancy and were not eating well or taking a prenatal vitamin may not have gotten adequate folic acid intake. Although these babies are probably also fine, some of these women might prefer extra scans for birth defects.
Women who have hypothyroidism (low thyroid levels) may also be at more risk for birth defects, especially if they are not treated or are undermedicated. These women may also wish additional scans if they are concerned. Again, this is by no means required, but it is an option.
Please note that even if you are at a somewhat increased risk for problems, that does not mean that there will be problems. Even in the above situations, most women still have healthy babies; if you fall into a category that might be more at risk, don't panic. Chances are that everything is okay.
Contrary to the opinion of some medical professionals, heavy women do not have to undergo multiple, detailed ultrasounds simply because of a slightly increased risk for birth defects. It is an option if women desire it, but it is NOT a requirement. Simply because you are large does not mean you must have ANY ultrasounds, let alone multiple ultrasounds to look for birth defects.
Instead, make your decision about ultrasounds based on what you would do with that information and your feelings about abortion, just like any other woman. Remember, the underlying implication behind doing lots of tests for birth defects is that there will be very strong pressure to abort if any problems are found.
Don't let anyone pressure you into scans you do not wish to have just because of your size. Base your decisions instead on your perception of your own risk levels, your feelings about birth defects, and what you would do if the baby did have a birth defect. In short, while size may be a co-factor in your decision to have additional scans in some cases, it should NOT be the only factor in your decision.
Dating the Pregnancy
Ultrasounds for dating the pregnancy can be a mixed blessing in women of size. They can be both helpful and hurtful. It depends on the exact situation whether extra ultrasounds for this purpose are justifiable.
Some providers want to do an automatic ultrasound in big moms in order to date the pregnancy. They don't trust a big woman's report of her last menstrual period for dating because they assume most big women have irregular cycles. They also don't trust traditional measurement techniques for tracking a baby's size and progress because of the mother's size.
For example, What To Expect When You're Expecting states, "Accurate dating of a pregnancy may be tricky because ovulation is often erratic in obese women and because some of the yardsticks doctors traditionally use to estimate the date (the height of the fundus, the size of the uterus) may be made indecipherable by layers of fat."
This is NONSENSE. *If* a woman's cycle is erratic or longer than usual, THEN a dating ultrasound may be justified. But to automatically do it for every large woman simply based on her size and an assumption of potential problems is ridiculous and discriminatory. Many large women have perfectly regular cycles, and to require an automatic dating ultrasound in every big woman because some have erratic cycles is illogical and unnecessary. And it is not true that fundal height and size are "made indecipherable by layers of fat;" a good provider can measure fundal height and knows how to compensate for a larger woman's size (see below) in measurements.
It's not that dating ultrasounds can never be useful in larger women, just that it should be done ONLY in those who have an indication for it, such as very irregular or extra-long cycles. This is not an issue of size, it's an issue of true indications. Doctors should use the same indications for performing a dating ultrasound in big women as they would use in women of average size.
Ultrasounds to date the pregnancy should not be done automatically in women of size. In most cases, they are not necessary, and thus do not justify exposing vulnerable first-trimester fetuses to the possible risks of early ultrasound. However, in some cases, dating the pregnancy can be useful. In these cases, the tradeoffs may make any possible exposure more justifiable.
For example, some heavy women have Poly Cystic Ovarian Syndrome (PCOS), which often causes irregular menstrual cycles and infertility. Sometimes women with PCOS ovulate without realizing it, get pregnant, and then do not know that they are pregnant because it's not unusual for them to miss their period. So in women with extremely irregular cycles, ultrasound to help date the pregnancy can be very helpful. This is true for women of any size, but there may be a subgroup of big women with PCOS that may find this procedure especially useful.
Some big moms tend to have longer-than-average menstrual cycles. This will affect the gestational age of their baby, making it younger than it "should" be by Last Menstrual Period (LMP). Instead of ovulating on day 14, for example, they may not ovulate till day 21 or even later, and their due dates should be moved later accordingly. (Readers should also note that a longer cycle will also affect the accuracy of the AFP test as well.) In these women, a dating ultrasound may be useful, but in most cases it is probably not necessary and should not be mandatory.
If a woman has 35 day cycles that are very regular, then a provider should automatically adjust the due date back one week. Exposing the fetus to ultrasound is not necessary; it is obvious from the woman's cycle that she ovulates later than usual, and the due date should be adjusted. Unfortunately, many providers refuse to change a due date based only on a longer menstrual cycle, even when she has proof of later ovulation through fertility charting. Thus, in this case, very early ultrasound (with its more accurate dating) might help providers believe that the due date should be moved later. (However, if a provider refuses to credit that you know when you ovulated or that you have longer cycles, it may be a good sign that you need to change providers!)
On the other hand, keep in mind that even a very early ultrasound can be "off" by a week, and so a provider may not change a woman's due date based simply on such an ultrasound. Then the baby has been exposed to all that ultrasound at a very early age, and for no real benefit. So this use of ultrasound can be a mixed blessing and may not be worth the ultrasound exposure.
Ultrasound pregnancy dating is most accurate in the first trimester, when there is very little biological size diversity. Ultrasounds set at this time generally are accurate to within a week or so. Ultrasounds in the second trimester are less accurate because babies start to grow at different rates, but are generally accurate within two weeks, plus or minus. If a doctor tries to "move up" your due date 1-2 weeks based on an ultrasound in the second trimester, this is within the dating window and the due date shouldn't be changed. If your dates were off by 6 weeks, on the other hand, an ultrasound in the second trimester should be able to detect that and changing the due date makes sense.
In women who tend to have bigger babies, using ultrasound for dating later in pregnancy can lead to doctors moving up a woman's due dates unnecessarily. This can lead to significant risks for the baby from prematurity, impede breastfeeding, and increase the risk for unnecessary cesarean in the mother. If you are very sure about your LMP dates and/or conception dates, be very hesitant to move your due date based on a second trimester ultrasound unless there are major discrepancies. If you are unsure about your dates or if you tend to be somewhat irregular, then a change may be more justifiable.
No due dates should be changed based on ultrasounds from the third trimester, which can be off by three weeks. There is far too much biological growth diversity at this point for gestational age to be pinpointed exactly, and bigger-than-average babies often "appear" to be farther along based on femur length and other measurements. This often leads to babies being induced or sectioned prematurely, and all the health risks this entails. Unless there are major extenuating circumstances, beware moving your due date based on a third trimester ultrasound.
Danielle's Story: I was 7.5 months pregnant when I arrived from overseas to have our baby at home in New Zealand. The hospital decided to do their own testing, and after yet another ultrasound they came to the conclusion that our baby was due on the 23rd of November even though my last menstrual cycle and doctors in Australia told us our baby was due around the 16th of December. Being our first pregnancy, we decided the hospital must be right and we continued with our near perfect pregnancy.
At "8.5 months" it turned out our daughter was still breech; in fact the specialist said he could not turn her manually because she had descended down feet-first into my pelvis...We decided the only way to ensure our baby was out safely was to have a cesarean. Wednesday the 13th of November at 8 a.m. was the date of our little baby's birth. It was a weird feeling knowing what day and at what time your baby's birthday will be.
She had problems breastfeeding. She stopped breathing and nurses rushed in and told me she had mucus on her lungs. They informed me the only way they could get rid of the mucus was "to give her a bottle of formula." Later that night, the baby woke hungry. I tried for more than hour to feed her by myself, but she just would not latch on. Things did improve at home, but our daughter never breastfed. After trying for 9 weeks of pumps, syringes, bottles, sterilizing, breast shells, shields, and crying, we decided to give up.
It turned out we were right---she was 3 weeks early at birth [Kmom note: More like a month!]. Because my husband is 6 ft. 4 and I am 5 ft. 11 all the ultrasounds showed her to be bigger and taller than she was. I don't regret the c/s but I do regret having her early because I now can't help thinking if we waited, she would probably have turned, and I would have had a 'normal' birth and not had such troubles breastfeeding.
Kmom's Notes: Elective cesarean on its own is a risk factor for breathing problems; elective cesarean plus prematurity is an even stronger risk for breathing problems. It also often impacts a baby's ability to suck effectively; it is not easy to preserve breastfeeding in the face of prematurity. Changing a due date late in pregnancy is highly questionable and may have serious health implications.
Although many providers automatically book a big mom for an ultrasound to determine dates, this is unnecessary and sizist treatment for most big moms. Extra ultrasounds for dating a pregnancy may be necessary in some big moms, just as it is in some average-sized moms, based on indications like very irregular or longer-than-average cycles. But it should not be done automatically, based only on a woman's size.
Big moms should also be particularly cautious about changing their due date based on ultrasounds from later in pregnancy. Because some big moms tend to have big babies, and because ultrasound fetal age estimation is based on averages of size, some bigger babies may be estimated to be older than they actually are. This can lead to early delivery and many complications.
Checking for Fetal Position
Some providers will tell heavy women that they cannot tell the baby's position because of the woman's fat, and will order extra ultrasounds near term to determine the baby's position. The authors of What To Expect When You're Expecting, for example, state, "An overly padded abdomen can also make it impossible for the doctor to determine a fetus’s size and position manually, so that technological assistance might be necessary to avoid surprises during delivery."
In Kmom's opinion, this is also nonsense. An ultrasound for this reason should not be necessary in most cases; a skilled provider SHOULD be able to tell whether the baby is vertex (head down), breech (bottom or feet first), or transverse (lying sideways), even in heavy women. Although it might be more difficult, a doctor or midwife who knows their stuff SHOULD be able to detect a baby's position even in a so-called "overly padded" abdomen. If your provider tells you that they cannot do so because of your size, you should question their competence to see women of size at all! Clearly they are not well-trained in adapting typical procedures for women of size, and clearly they believe that big moms are abnormal, need high-tech help for birth, and cannot be treated normally. Chances are you will end up with an unnecessary cesarean with this type of provider.
To be fair, though, there may be two exceptions where ultrasound for fetal position may be helpful, however. In a few extremely heavy women, the mother's "extra padding" is so extensive that it becomes difficult to palpate thoroughly. But this is usually the exception rather than the rule. Most of the time, a skilled provider can palpate the baby's position just fine in women of size without exposing the baby to more ultrasound. Still, once in a while, it may become necessary.
Second, sometimes an irregularity in the baby's position makes it more difficult to detect fetal landmarks, and thus ultrasound might become justified. Sometimes the provider suspects that the baby is head-down but in a less-optimal position for birth, such as posterior (facing the mother's tummy), asynclitic (head tilted), or compound (hand or arm by head), and may order an extra ultrasound in order to know for sure.
Baby malpositions may be more common in women of size, and this can cause more difficult labors, a great deal of intervention, and many cesareans. A good provider knows that finding out the baby's position ahead of time and then taking measures to try and help the baby resolve its position before labor starts (or during early labor) can prevent a lot of problems later on in labor. Thus an extra ultrasound in this situation may clearly present more benefits than risks, if the provider uses that information to help the baby resolve its position. An ultrasound showing a malpositioned baby should not be used as an excuse for an elective cesarean, as there are things that can be done to help a baby turn. (Chiropractic care can often help resolve fetal malpositions, or Optimal Foetal Positioning tricks can help turn babies too. See the Malpositions FAQ for more information.)
Routine ultrasounds done because a provider does not believe fetal position can be palpated in obese women are unnecessary and fat-phobic. However, there may sometimes be occasions when an extra ultrasound is justified if the mother is truly supersized, fetal position really is unclear, or if ultrasound discovers a malposition and this information is used to help resolve the baby's position. Each situation must be judged on a case-by-case basis. [For more information on fetal malpositions, how they can impact labor, and how they can be prevented/fixed, click here.]
Tracking the Baby's Growth
Some doctors and midwives believe that because of a big mother's extra abdominal padding, there will be no way to accurately track the growth of the baby without multiple serial ultrasounds. Again, What to Expect When You're Expecting reflects this common prejudice when they state, "Some of the yardsticks doctors traditionally use...(the height of the fundus, the size of the uterus) may be made indecipherable by layers of fat."
Poppycock! In Kmom's opinion, this is not a justifiable use of ultrasounds and reflects poor training and biased attitudes. MOST providers who are well-trained can detect the height of the fundus (top of the uterus) and size of the uterus perfectly fine; providers who are well-trained do NOT usually find these things to be "made indecipherable by layers of fat." That's just an excuse for sizism.
In most pregnant women, providers measure the mother's fundal height (from the pubic bone to the top of the uterus), which in the third trimester roughly corresponds with the number of weeks she is pregnant (i.e. 35 weeks = 35 cm). It is true that a big mom's measurements probably will be larger than average, but it does NOT mean that the baby's growth cannot be tracked, or that multiple ultrasound scans for growth are needed. Fundal height CAN be used in women of size, provided some common sense is used.
On the one hand, some providers contend that fundal height measurements are totally useless in fat women and don't even attempt to do them, relying instead on ultrasound, which as we see below, is already not very accurate. On the other hand, other providers regularly do fundal height measurements in women of size but expect them to measure the same as every other woman. Then when the measurements are larger, they panic that the baby is huge and order extra ultrasounds, early induction, or elective cesarean. Both of these approaches are quite common, and both are equally size-phobic.
The truth is that you CAN do fundal height measurements on fat women. It helps to have a woman with a large "apron" (belly) hold that belly up and away from the pubic area; this often makes the fundal height measurement a bit more accurate. However, you should not expect these measurements to conform to the traditional standards of 35 cm = 35 weeks. A size 26 woman is NOT going to have the same fundal height measurement as a size 5 woman, and to expect otherwise is ludicrous! A size 26 woman has more abdominal 'fluff' which will increase the fundal height measurement. This is only logical and natural.
Fundal height measurements are NOT irrelevant or useless in women of size, just because the measurement will be bigger! What doctors should do is compare the CONSISTENCY of fundal height measurements in a big mom from week to week. If a big mom is always 4 cm "over" the expected fundal height measurement from week to week, then this is a good indication of normal sustained fetal growth, and there is no need for extra ultrasounds. If a mother is usually 4 cm "over" and then suddenly is 10 cm "over," this would be a sign for significant concern and probably would indicate the need for a further ultrasound.
Similarly, simply because a big mom's fundal height measurement is over the expected fundal measurement for that week does NOT mean that this mom is going to have a huge baby. A big mom's abdominal fat will add to the measurement but this does not necessarily indicate extra fetal size. Most big moms measure >40 cm at 40 weeks. Although big moms have a higher rate of bigger babies, the majority (about 70-80%) still have average-sized babies, despite larger fundal height measurements.
Even if a provider suspects that their client may be part of the 20-30% of big moms that have a bigger baby, research shows that this is NO reason for early induction or elective cesarean unless the baby is over 11 lbs. or the mother is diabetic. As noted below, early induction for suspected macrosomia often increases the cesarean rate to more than 50%!! And many studies have noted that the risks outweigh the possible benefits in elective cesareans for macrosomia. So management should not change, even if a provider thinks a woman might be carrying a big baby. Interventions do not help, and they often worsen the outcome.
If your provider seems excessively concerned over a larger than average fundal height measurement, or requires multiple ultrasounds in order to track the baby's growth in a normal pregnancy, then your provider is probably not size-friendly and you may want to strongly consider finding a new provider, no matter how far along you are. Similarly, if a provider believes that extra ultrasounds are necessary and that there is no way to tell a baby's size or position 'through all that fat,' it probably reflects a strong fat-phobic bias on the part of the provider, and is a good sign that a woman should switch providers if at all possible.
Other than realizing the fundal height numbers will probably be a little different, there is no reason to treat large women any differently when tracking fetal growth. If your provider can track fetal growth without serial ultrasounds in women of average size, then they should be able to do it in women of size as well. Furthermore, most big moms report that they are not required to take extra ultrasounds for tracking fetal growth, so obviously some providers have learned how to track fetal growth adequately despite size! If some providers can do it adequately in women of size, then there is no need for other providers to order extra ultrasounds for this reason in large women.
Extra ultrasounds to measure fetal growth is NOT necessary in women of size unless there are co-existing medical complications like pre-eclampsia, diabetes, etc. Routine serial ultrasound to track fetal growth exposes babies to a great deal of extra ultrasound and often lead to harmful interventions like induction for macrosomia. They are unnecessary and potentially harmful, and should not be done in most cases.
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 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, birth trauma, and lawsuits.
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 fetal 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 often 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. 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 Estimating Fetal Size in Large Moms
Because a larger baby is more common in large moms, because obesity combined with a big baby is a risk factor for shoulder dystocia, and because doctors get sued frequently for birth injuries, many doctors require virtually all of their large mothers to have an ultrasound estimation of size near term. Then if the ultrasound predicts a big baby (or the doctor still suspects one despite the ultrasound), the doctor either pressures the big mom for an elective cesarean or an early induction. This is one of the most common care scenarios that big moms face, and one probably responsible for the high rate of cesareans in women of size.
MOST large moms don't have big babies, and MOST big babies are born vaginally without shoulder dystocia. Acting as if a big baby and shoulder dystocia is a sure thing in a big mom projects the risk of a small subgroup onto the whole group. This does not improve risk outcome; in fact, it often worsens it. It also ignores the fact that labor management practices like early induction, forceps, fundal pressure, and less-optimal birth positions increase the risk for shoulder dystocia and birth injuries unnecessarily, and that changing labor management practices could substantially reduce the risk for birth injuries.
Are ultrasounds for estimating fetal size accurate in women of size? Some doctors order ultrasounds in big moms to estimate size, and when the estimate says the baby is average-sized, they contend that ultrasounds cannot be trusted to truly estimate fetal size in big women, and to "be on the safe side" they should induce early. Some books and doctors have contended that because ultrasounds for diagnosing fetal abnormalities can be more difficult to image fully, estimates of fetal size in big moms may also be less accurate. The pregnancy book, Carrying A Little Extra, states, "The accuracy of ultrasound measurements is decreased when this test is performed through a large fatty layer, which makes it more difficult to determine the baby's weight and status."
While it is true that birth defects can be harder to detect because of a "large fatty layer," it is NOT more difficult to determine the baby's weight. Several studies (Shamley and Landon 1994, Field 1995, Farrell 2002) have confirmed that ultrasound fetal weight estimates are as accurate in women of size as they are in women of average size, even though that's not saying much. Farrell (2002) concludes:
Our study suggests that the effect of maternal BMI on...estimates of fetal weight is minimal and is likely of little clinical significance...Despite this, errors in weight estimation of [plus or minus] 20% are possible and must be borne in mind when decisions regarding obstetric management are formulated.
Shoulder Dystocia Risks in Big Moms
Doctors have long assumed that the obese mother is at increased risk for shoulder dystocia, even if the baby is of normal size. They believe that the maternal pelvis is padded with extra fat, and that this can prevent a baby from moving down or getting out. They call this Soft Tissue Dystocia. Dr. Mortimer Rosen, writing in The Cesarean Myth, states,
[Obese] patients often have what we call 'soft tissue dystocia'--they're fat on the inside, too, and the tissue inside obstructs the baby.
However, this idea of Soft Tissue Dystocia does NOT seem to be based on research, but rather on long-held and commonly-taught traditional assumptions. The truth is that doctors do not KNOW if the pelvises of fat women are more obstructed by fat and that this prevents babies from being born vaginally, they just assume that it is so. In fact, one study that looked at the question of soft tissue dystocia (Wischnik, 1992) did NOT find the pelvic outlet dimensions of fat women to be significantly affected. They wrote:
The common assumption can no longer be maintained, that adiposity necessarily causes soft tissue [dystocia] due to larger fat compartments within the small pelvis.
Think about it. If the "padded pelvis" theory were true, then you'd never see a 300 or 400 pound woman give birth vaginally, because there would be so much fat in there that no baby could fit through. But this website contains stories of women well over 300 lbs. (and even over 400 lbs.) giving birth vaginally. So obviously even very fat women with very "padded pelvises" can and HAVE given birth vaginally, and without shoulder dystocia.
However, if a big woman's size was relevant internally and externally, then what makes more sense is to be sure that big mothers labor and give birth UPRIGHT or on their hands and knees. This would permit gravity to help do the work, open the pelvis wider and get the tailbone and sacrum out or the way, and make the woman's weight work for her to help press the baby down and out.
And remember, if there is some fat in the pelvis, it's not like bone. Fat is highly malleable and movable; it is doubtful it would block the way for the baby to get out. If the mother stands up and uses gravity and her own weight to help the baby move down, any theoretical internal fat that might be present will get squeezed out of the way and the baby will move down anyhow.
Because of the unproven theory of soft tissue dystocia, some doctors assume that obesity predisposes a mother to shoulder dystocia, even with a small baby. However, a recent study (Robinson 2003) shows that this is not true. It found:
Maternal obesity was not significant as an independent risk factor for shoulder dystocia after adjusting for confounding variables...The strongest predictors of shoulder dystocia are related to fetal macrosomia. For obese nondiabetic women carrying fetuses whose weights are estimated to be within normal limits, there is no increased risk of shoulder dystocia.
This study found that the biggest risks for shoulder dystocia were for big babies (especially babies over 10 lbs.), babies of women with diabetes, and "midpelvic instrumental delivery" (i.e. mid-forceps). The study found that neither postdates pregnancy, obesity, nor prolonged pushing stage were significant predictors of shoulder dystocia after analysis for confounding variables. Other studies (Nocon 1998, Lewis 1998) have also found that obesity was not independently associated with shoulder dystocia.
It is true that a higher proportion of big moms have big babies, and that big babies are at increased risk for shoulder dystocia. It is also true that obese women are at higher risk for diabetes (gestational and type 2 diabetes), and that diabetes increases the risk for shoulder dystocia. However, MOST big moms do NOT have big babies (70-80% have average-sized babies), and MOST big moms do not get diabetes or gestational diabetes in pregnancy (about 70-80% do not). So most big moms are not at increased risk for shoulder dystocia.
Thus, if a doctor assumes that an obese woman is at very high risk for shoulder dystocia simply because of maternal size or a "padded pelvis," he is wrong. MOST big women will not have big babies, and most will not have diabetes of any type. An early induction or elective cesarean simply because of shoulder dystocia fears is unjustified in most big moms when it is only based on their size.
However, in the subgroup of big women who have diabetes and a large baby, the risk for shoulder dystocia is significantly increased. Thus increased surveillance and interventions in this group may be more justified than in other groups of heavy women. However, even in this group, research has found interventions to be questionable below a fetal weight of about 10 lbs. (see the FAQ on GD: Basic Treatment Protocols for more information), so it is by no means certain that the most optimal course is intervention, even in this group.
A very large weight gain during pregnancy has been found by several studies to be significant risk factor for large babies and for shoulder dystocia. Thus, in large women who have gained a great deal of weight in pregnancy, increased surveillance might also be more justified. Exactly how much weight gain should trigger such surveillance, however, is unclear.
Little is known about the risks of shoulder dystocia in obese women who are suspected to have big babies after a normal weight gain. No research has been done to see if the risk of shoulder dystocia is increased more when macrosomia and obesity are present (beyond the risks of macrosomia itself), nor has research been done to test the best course of action in this group (expectant management or early intervention). For clues on what to do in this situation, we can only look to generalized macrosomia research and extrapolate.
Macrosomia research has found that in most cases, expectant management (waiting for spontaneous labor) is best. Intervention (like early induction) actually causes more harm than good in many studies. And in fact, induction and elective cesareans carry serious risks for morbidity that must be considered as well. This is why the latest clinical management guidelines for macrosomia from the American College of Obstetricians and Gynecologists (2000) state:
Thus, unless it is proven that the presence of obesity should alter these recommendations, expectant management should be the course of action for nondiabetic obese women with a suspected big baby. As a precaution, women and their providers may want to carefully avoid factors that may increase the risk for shoulder dystocia (like epidurals, forceps, vacuum extractor, pushing on the back or semi-sitting, etc.).
Making Care Decisions When a Big Baby is Suspected
The big mom near term whose doctor or midwife is concerned about fetal macrosomia faces a lot of difficult decisions. They are usually strongly pressured to have an ultrasound to estimate fetal weight, and face the difficult decision of whether to induce early, have an elective cesarean, or await spontaneous labor. Often, these moms are scared into interventions by being told horror stories about shoulder dystocia, birth injuries, and possible death, without being told that the actual risk of this is quite low, and that management practices have a lot to do with its occurrence.
Shoulder dystocia risks are real, and sometimes there are poor outcomes as a result of shoulder dystocia. However, sometimes there are also bad outcomes after an induction or elective cesarean as well. Doctors tend to discount the risks of induction and cesarean, but they DO exist and are not insignificant. The problem is that the risks of both shoulder dystocia and induction/cesarean are small but not insignificant. This is what makes the choice of what to do so difficult. Either way lies some degree of risk.
At this time, most research indicates that interventions for
macrosomia are not justified. Sacks and Chen (2000), in an extensive review of
macrosomia and shoulder dystocia research, concluded, “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.”
Sandmire, 1993, states unequivocally that:
Even if clinicians could determine fetal weight accurately, the frequency of persistent fetal injuries associated with vaginal birth of the macrosomic fetus is so low that induction of labor or cesarean birth is not justified on that basis...In any event, the clinician who decides, based on a suspicion of macrosomia, to induce labor or deliver by cesarean puts the mother at unnecessary risk of adverse outcomes associated with these interventions.
Delpapa (1991) found that “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."
Yet despite CONSIDERABLE evidence against the practice of size estimates and induction/cesarean for big babies, many large moms are pressured into early induction or elective cesarean. Because being sued is more common after shoulder dystocia (and because they don't realize how much shoulder dystocia can be prevented by changing management practices), doctors usually err on the side of choosing induction or cesarean, despite all the evidence against this.
If your doctor wants you to do an ultrasound for estimating fetal weight, remember that this estimate is especially inaccurate in bigger babies, that a prediction of macrosomia (true or not) results in a very high cesarean rate, that even doing an ultrasound for size at all results in higher cesarean rates, and that interventions for macrosomia actually present more risk than benefit.
Be VERY cautious about making important medical decisions (like inductions or elective cesarean) based solely on dubious data like fetal weight estimates. If your provider insists that you must have an ultrasound to estimate fetal size, this may be an indication that you need to switch providers. Unless you are diabetic or there are extenuating circumstances, research does NOT support estimating fetal size ahead of time or interventions based on this. Any provider who does not know this is either not familiar with current research or chooses to ignore it, both of which are ominous signs in a provider.
Estimated fetal weight ultrasounds (and the accompanying induction) are the most common interventions in women of size, and one that probably raises the cesarean rate among big moms tremendously. Here are a few stories of big women's experiences with ultrasound for estimated fetal weight. There are more later on in this FAQ as well.
Lisa's Story: They estimated my son to be 8.5 lbs. at 35 weeks, and when he was born a day later, he was 6.6 lbs.
L.M.'s Story: I had an ultrasound around 36.5 weeks to estimate fetal weight. The result the technician gave was "about 7.5 lbs." My OB, who had told me from the very beginning that I should expect a big baby, said the results could be off by as much as a pound. He then said that he really thought the baby was more like 8.5 lbs. already and that if we went full term she would definitely be over 10. A few days later I was induced (having GD and pre-eclampsia contributed to their desire to induce). After the induction failed, my darling daughter was delivered via c-section, weighing a whopping 5 lbs. 11 oz.!
Sharon C's Story: I knew the day/time of my daughter's conception...At 41.5 weeks I had a second ultrasound, just to check size and make sure everything was okay in there, as I was "postdates." The ultrasound tech was very nice, gentle and saw everything she wanted to see quickly and easily.
BUT she did measurements of the baby's leg bone, did some calculations, and estimated that the baby weighed in excess of 13 pounds at that time. She called in the doc, who checked the measurement and then the calculations and concurred, saying that if I went into the next week, the baby would be over 14 lbs., as "they grow at least a pound a week, you know."
I was, as you can imagine, a little concerned about pushing a baby THAT huge out, but figured that there wasn't anything I could do about it. I had been in pre-term labor from about week 22, and here I was, a week and a half "postdates." So I knew that when the baby was ready, it would come, and not before.
Well, another week went by, still no labor, so underwent induction with laminaria insertion the night before...waaaaaaay too much pitocin, and finally had a C-section due to poor labor management (IMO) and failure to progress. Never dilated more than 3 cm after 18.5 hours on the pit. Ugh.
But, my wonderful darling daughter was only 8 lbs. 8 oz., skinny as all get out but with very, very long legs (and arms, and fingers and toes----takes after my side of the family!). They had not done a measurement of anything other than the leg bones for the estimated weight calculations! I was relieved, as I was concerned that such a large baby could mean problems we had not foreseen. She was perfect, too long for the newborn clothing that we had, but just perfect.
However, it's important to note that ultrasound estimates are not always wrong. Sometimes big moms really do have bigger kids, and sometimes the ultrasound predicts this accurately! If the ultrasounds for estimating size are wrong half the time, they are right half the time too. But you might as well just flip a coin to figure out whether or not the baby is macrosomic.
Veronica's Story: My 20 week ultrasound was normal, except the tech mentioned he had a short femur. He predicted our child would be short. Fast forwards to 38 weeks. My pregnancy had been completely uneventful. No complications at all. The doctor in my group of 5 that I felt was the least "fat friendly" was the doctor for this appointment. After a brief visit she announced to me she thought this baby was getting big and she wanted me to get an ultrasound to estimate weight. I was surprised and thought it must be because she always seemed to be looking for complications. Anyway I decided to go through with the ultrasound, and the tech's estimate was 7 to 7.5 lbs. Of course with a plus or minus of a pound. Normal weight.
Strangely enough the tech mentioned that she had measured the same at 38 weeks and had a baby that was over 10 lbs. She said, "Ultrasound is just not accurate for estimating size." I asked her why doctors would send women for the ultrasound if it was that inaccurate. She, [an ultrasound tech] who does this every day, said, "I have no idea." I just let it go.
At my 39 week appointment, the senior doctor in the group seemed very surprised and almost annoyed that the other doctor had sent me for an ultrasound. He said 7 to 7.5 is what he'd estimated from my size and measurements. He sent me home feeling almost vindicated, as if the other doctor had done something wrong and he was right and I was right.
At 41 weeks, 4 days they decided to send me for another, in case I needed to be induced. Just in case, they said. I agreed. That tech, at a completely different facility than the first two, gave me an estimate of 8 lbs. 14 oz. If you figure a half pound a week growth, that matched the first estimate from a little over 3 weeks earlier.
I wound up beginning my induction that evening because the ultrasound detected a lack of "tone" or small hand movements. Baby was born 41 weeks and 5 days at 10 lbs., 9 oz. He had a 14.5 inch head and was 22.5 inches long. Not short and not small at all! He was much bigger than all the estimates. Turns out that one doctor I didn't trust was the only one who was right.
Even if the baby is going to be big, though, that doesn't mean that induction will increase your chances for a vaginal birth, as most doctors assume. In fact, it usually decreases your chances in most studies (see above).
And even if the baby really is big, it doesn't mean you can't have a vaginal birth! Although there is a higher cesarean rate and/or birth trauma rate with big babies, most big babies are born vaginally and without problems, especially if not induced. Delpapa and Mueller-Heubach (1991) found that 72% of the babies predicted to be big were born vaginally if given the chance.
Katie's Story: My doctor never seemed concerned about me having a big baby. Even when my fundal measurement put me at a whopping 52 weeks, my doctor just explained it was because of the belly I had before I even got pregnant, and it had little to do with the baby's size. I had a few extra ultrasounds, but they were for other reasons, never requested by the doctor.
At 32 weeks, my daughter was estimated to be 5 lbs. 12 oz. Both the ultrasound technician and my doctor said that I was going to have a big baby, definitely over 9 lbs. Throughout the last 2 months of my pregnancy, my doctor and I talked often about my "big baby" but no one ever mentioned the possibility of not being able to birth her naturally. It was almost like it was assumed that I'd have no problems. That gave me a lot of confidence.
In the end, she was born weighing 10 lbs., 3 oz., and I did indeed birth her naturally with no problems except a third degree tear (no episiotomy) which healed without problems as well. I'm ready to do it again.
Lessening the Risk for Shoulder Dystocia
Although shoulder dystocia is a legitimate concern with bigger babies, most big babies don't have shoulder dystocia. There have been some very large babies born without shoulder dystocia or any birth trauma at all! The problem is that there are no guarantees of that, and that makes doctors nervous. Even though birth injuries are unusual even in big babies, they operate from a "worst case scenario" mentality and want to intervene.
The shoulder dystocia issue is NOT just about baby size. It's also about labor management. It is clear from research that some procedures strongly increase the risk for shoulder dystocia. For example, using forceps during labor DOUBLES the rate of shoulder dystocia in some studies (Nesbitt, 1998). Fundal pressure (pushing on the top of the uterus) also increases the risk for problems (Gross 1987). Induced labor also increases the rate of shoulder dystocia in some studies (Combs 1993, Jazayeri 1999, Nesbitt 1998), probably because the painful inductions lead to more epidurals, and epidurals cause more forceps births.
Many midwives also believe that the common OB practice of rushing the baby out once the head has crowned also increases the shoulder dystocia rate. They believe that the pulling, pushing, and twisting doctors do to quickly get the baby out may actually get some babies 'stuck' instead. As an alternative, many midwives prefer letting the baby rotate on its own and come with the next contraction instead of being pulled, pushed, and twisted out between contractions. They believe that most of the time, the baby and the mother's body work together to find the baby's own safest way out, and interfering with or rushing that process can cause complications, especially with a big baby.
There are certain things that the mother can do that may lower the risk for shoulder dystocia even more. Although these need further evaluation and validation with well-designed, large studies, these techniques have been anecdotally reported by midwives to improve outcome, and a few have begun to be reported in research as well (Nixon 1998, Bruner 1998). They include:
Probably the most important factor in preventing birth injuries when shoulder dystocia does occur is having a provider that is well-rehearsed in the best techniques for managing shoulder dystocia. In fact, most studies state that rather than inducing early or doing elective cesareans, the best way to reduce the incidence of birth injuries is to have providers be more well-prepared to handle a shoulder dystocia, and to know which techniques minimize morbidity. Delpapa and Mueller-Heubach (1991) state:
It would seem that prevention of morbidity would be best accomplished by proper and immediate management of shoulder dystocia once it occurs. [Other studies] found a relationship between the maneuvers used to relieve shoulder dystocia and the incidence of neonatal complications.
Birth injuries are much more likely to occur if a provider panics and starts pulling or twisting the baby, or pushes on the top of the uterus to get the baby out (Gross 1987). Unfortunately, many OBs are poorly trained in management of shoulder dystocia and make the problem worse. Midwives tend to be more familiar with techniques that help lower the rate of birth injuries.
For example, most midwives know that simply switching birth positions is one of the simplest and most effective ways to get the baby out safely. This helps shift the pelvis around, and may even increase the pelvic dimensions. Having the mother stand up, roll over to all-fours position, flex her knees up to her ears, arch her back strongly, or shift her hips from side to side is often enough to disimpact most babies without resorting to the more invasive techniques many OBs are taught to use first.
Bruner (1998) documents that moving the mother to the
all-fours position (mother on her hands and knees) resolved 83% of shoulder
dystocias without further maneuvers, and avoided virtually all morbidity
commonly associated with shoulder dystocia. The authors (including two
MDs) concluded, "The all-fours
maneuver appears to be a rapid, safe and effective technique for reducing
shoulder dystocia in laboring women.”
Some doctors may be reluctant to use the all-fours maneuver because the majority of women they attend are drugged and thus slow or unsteady to move at a time when quick action is important. Women with epidurals are effectively paralyzed from the waist down and may not be able to roll over onto their knees at all. This is a good argument for NOT having an epidural or other drugs if a big baby is suspected, rather than an argument against the Gaskin maneuver!
However, if there is an epidural or drugs present, another effective maneuver is the McRoberts maneuver, where the obstetric assistants flex the mother's hips strongly and bring her knees up to her ears. This changes the angle of the mother's pelvis and often easily disimpacts the baby's shoulders. This maneuver has been shown to be effective in most cases and can be used even when a woman has had an epidural.
If neither the all-fours position nor the McRoberts maneuver resolve the shoulder dystocia, the doctor or midwife can push down on the pubic symphysis joint (suprapubic pressure) and dislodge the shoulders that way. Or they can reach inside the mother, turn the baby to a diagonal plane (which offers more room physiologically) and get the baby out that way. Or they can grasp the baby's arm and sweep it across and out to reduce the size of the shoulder's dimensions. However, these procedures are associated with increasing amounts of problems and fetal injury compared to the all-fours (Gaskin) maneuver and the McRoberts maneuver, so they should only be tried AFTER the other procedures have been attempted.
If you suspect you have a big baby, you may want to re-evaluate your provider's attitude and knowledge about big babies. If the provider seems excessively preoccupied with the risks of big babies and spends a lot of time scaring you about what he/she thinks will happen, this is a sign that this provider is very fearful of big babies and probably would not handle a shoulder dystocia well if it occurred. Instead, you might want to consider finding a provider that is not afraid of big babies, does not suggest interventions for big babies, and is well-versed and comfortable in handling problems should they occur.
Mothers with a suspected big baby face choices that are not easy to make. Although doctors tend to emphasize only the risks of shoulder dystocia, in truth all options have risk tradeoffs. Although the risk for shoulder dystocia and birth injuries with big babies is increased and care IS needed, the risks of interventions such as induction or elective cesarean are also significant, and usually do not prevent poor outcome. In fact, research shows that they often make it worse.
Although it is not possible to completely eliminate the risk of birth injuries, most of the time positioning and careful management can prevent or minimize most problems, and if problems occur during labor that indicate a higher risk for shoulder dystocia (such as a slow pushing stage or no descent of baby), a back-up cesarean can be performed then. This is why most studies recommend "expectant management" (i.e., awaiting spontaneous labor) with most cases of suspected macrosomia.
However, each mother must decide for herself what risks she is most comfortable with. She must weigh the benefits and risks of each possible course of action and decide what is best for herself and her baby.
Ultrasound Stories of Big Moms
The following are big women's stories of their ultrasound experience, both good and bad. And of course, there are more stories in the sections above about specific situations. Keep in mind that YOUR experience may vary.
The stories are told in women's exact words, although occasionally it was necessary to edit or summarize a few stories. Changes to the original story (other than spelling/grammar, and specifics about dates or people) are indicated by [brackets] or ellipses.... Occasionally a woman's story that Kmom has been told is repeated here, paraphrased and summarized in Kmom's words.
If you have an ultrasound story you would like to share for this FAQ, please email Kmom with the story (no attachments please!), how you want the story attributed (full name, first name only, initials, pseudonym, etc.). Please also be sure to include your permission to use the story.
"Good" Ultrasound Stories
Mary Ellen's Story: During my 2nd prenatal visit with my OB/GYN he suggested, or rather requested, that I go for an ultrasound at 19/20 weeks of pregnancy. He referred me to a "high risk" OB/GYN. I asked my dr. if he considered me "high risk" because of my weight or any other factors. He told me no, he was just sending me to the high risk dr. because he was the best and if there were any sort of problem he would pick up on it.
I scheduled my u/s for week 19 and they told me I didn't need to drink any water beforehand---they actually told me to try to limit my drinking before I came into the office. Everyone in the office from the receptionist to the Dr and his assistant treated me very well. My weight was never mentioned and I was very comfortable through the whole experience.
The Dr. easily picked up our baby on the u/s and took the time to show us and explain about all the important things he was looking for. There were no complications that he could see and everything was perfect.
Stephanie's First Story: I found out that I was pregnant in August. I went in for my first appointment in October. At that visit, I weighed 340, and the doctor did a vaginal ultrasound. We saw the little "Spud" and his little heart beat. At my next visit, the doctor tried to hear the heartbeat but she couldn't get it. So, she did another vaginal ultrasound. "Spud" looked more like a baby at that point. We could see his head, little arms, lets, and heart.
I didn't have another ultrasound until 20 weeks. This was an external ultrasound, and the technician was great! She saw pretty much everything she needed to see except she couldn't get a good picture of the spine or tell the sex very well. We did another one at 24 weeks. This one was very telling. The technician got everything she needed, and she told us we were having a boy.
Denise K's First Story: I am over 300 lbs, [and] was when I had my 18 week u/s and they clearly saw [my son's] parts. There also was no trouble with most of my u/s in finding the baby or finding his anatomical structures. I don't recall anyone going through my belly button, and I am a freak with regard to my belly button---If they had put the wand there, I'd remember.
Margery's Story: I had 4 [ultrasounds], right in my doctor's office. The techs there were wonderful. I was what my DH liked to call 'teacher's pet' there. My doctor used to call me the miracle pregnancy, because I was 378 lbs. when I got pregnant and it only took one cycle of Clomid/Glucophage to get pregnant (he thought at least 6 months). I did have some problems in December. They thought there was too much amniotic fluid, so they sent me over to the hospital for a better view. There I was treated fairly--I wouldn't say bad, but not good either. The tech was nice, but the doctor who read the u/s was put off by my weight just a little. He asked her how she found what she was looking for, because there was 'some excess weight here' (he did talk like I was not in the room). She was very nice and said if he just looked he would see exactly what she did...I was treated wonderfully at my practice.
Katie's Story: I had several ultrasounds during my pregnancy. Most of them were to reassure me because I wasn't able to feel much movement during the pregnancy. Turns out I just had a quiet baby (I often referred to her as "the sloth" for lack of movement). The ultrasound tech was fabulous. She was the one who explained to me that my inability to feel movement was partially my size but also because I had a front-lying placenta. It was sometimes difficult to see parts of the baby because of my size (particularly the genitals, which are more fleshy and thus harder to see). The ultrasounds never hurt, even when she had to put the wand-thingy deep into my belly button to get a good look.
Pressing Too Hard
Robin's Story: While I was getting a level II ultrasound done at 22 weeks, the technician was pressing unnecessarily hard. I complained and she said that it was going to be hard to get a clear picture through my "wall of fat." I got mad and told her that wasn't true and that getting a clear picture had to do with the skill of the technician. Needless to say, she pushed REALLY hard after that but didn't make any more comments. How rude!!
Kmom's Story: When I was pregnant with my 2nd baby, the OB used an office machine to do a quick ultrasound early in the second trimester. She pushed very hard, which was especially tender for me because it was right near my c-section scar from the first pregnancy. I protested, and she said she had to press hard in order to see anything. I suffered in silence. I have had other ultrasounds at about this stage in other pregnancies and they didn't hurt nearly so much; I think it was more her assumptions that caused her to press hard rather than any real need to do so. Nowadays, I generally avoid ultrasounds at that stage unless indicated, and when I do have an ultrasound later in pregnancy, I ask them to start off pressing easy and only increase pressure if really needed. This has worked well for me.
An Email Discussion: Remarks from Ultrasound Techs about a Woman's Size
Note From Kmom: Over the years I have heard from many women who complained about remarks that the ultrasound technicians made about their size, including:
- "Your weight is why I can't see anything. You might want to work on that."
- "I had a tech with my first pregnancy who had a hard time getting to the heartbeat because of the 'build of you people.' I was livid but bit my tongue."
- "I had one ultrasound tech complain to me and to an assistant he was going to have to do a vaginal ultrasound, and in a very huffy voice said, 'If these people weren't so LARGE I could do this NORMALLY!! No wonder the doctor couldn't hear a fetal heartbeat!' It may please you to know that this tech is no longer doing ultrasound at that hospital thanks to me!"
B's Story: I guess I was very lucky. I was over 275 [pounds] and had no problem. I went to the Ultrasound Institute which does just Ultrasounds, and all 5 turned out great. Plus when I went for my stress tests every other day for the last 3 months and their ultrasounds also worked great. I think it has to do with the tech's experience and their equipment. My nurses and techs and doctors were great. I started off from the very beginning telling them if they had a problem with my size then I would find someone else. Thank goodness my OB and her practice was not fat phobic and treated me as they would anyone else. I am also the type of person who expects the best or I give grief.
Michele's Story (in reply to other women's reported experiences): Boy, you ladies sure do have more restraint than I do! I would have been screaming...so loud that the whole place would have heard! I have had many, many ultrasounds and not once have I ever had a tech even imply that they couldn't see anything because of my weight and I weigh 350+. If any of them had ever made the "build of you people" or the "you need to work on that" comment I would have done my damnedest to have them fired or at least disciplined right then and there. Maybe when we, as overweight women, quit putting up with this crap it won't be as accepted as it is now...This subject just chaps my hide!
Misdiagnosed Tumor and Size Bias
"Tumor" Story: Kmom knows a woman online who was told she was not pregnant and that she had a very large tumor instead of a baby. She was about 80 lbs. 'overweight' and has just been scolded for being "irresponsible enough to get pregnant when this fat." After the consult he berated her for about an hour for being so "disgustingly fat" and that he was going to force her to diet so that her husband "would be able to stand to look at [her] again."
She had a vaginal ultrasound at about 12 weeks along, and this OB announced that she was NOT pregnant (despite the urine test results) because he could find no baby on the monitor. Then he told them he could see a very large tumor, that she needed surgery immediately, and would most likely have to have a hysterectomy. The mother shifted on the table, and suddenly it was clear that there was a baby in there after all. She changed providers, found out the baby was healthy, and that there was no tumor either. Her child was born safely the following year.
False Positive and Size Bias
Dawn's Story: I was a diabetic prior to becoming pregnant. When I went to get my level II ultrasound the tech could not get a good view of the baby's heart and spine because my son was hiding under my belly button. So she went to get the u/s doctor, and he never bothered to look himself...The doctor said right away that because they couldn't get a good view of the heart and spine that there was a high chance that the baby would have a massive heart attack during labor and would die. He said it would be caused from my obese weight and my diabetes. He even suggested that we consider having an abortion because the likelihood was great that this was going to happen. He said he could have a cardiac pediatrician evaluate the u/s but that they would come to the same conclusion.
We kept asking if there was something wrong in the u/s and they said no, but that they couldn't get a clear look. We had 2 weeks to decide about the abortion because legally you have up to 24 weeks to abort the baby. We were absolutely devastated. I cried and cried and he asked me why I was crying. He said he could understand my situation because he was overweight when he was young and had to lose weight. I said, "Have you ever been diabetic, overweight, and pregnant....impossible! So don't tell me you understand or can relate to how I'm feeling." JERK!!! When I went to the bathroom to pee and cry even more, he asked my DH if I was going to be okay. My DH said to him that he had just shattered every positive hope that I was having and how did he expect me to feel when he totally degraded me in front of the tech and my DH. We left and a few days later went to the OB.
I explained to her what happened and she told me she was never going to send me there again because I wasn't the first patient who ever came back crying due to his insensitivity. She said that the baby's heartrate was great and that the blood tests would have shown some distress with the development of the baby. She also said I was monitoring my diabetes with great care and what did he expect, for me to go on a diet [in pregnancy]?...So I never went to him again.
I always had fear about the condition of my baby but I was glad that I followed the advice of my OB and never went to him again...I gave birth to a healthy baby boy with no problems with his heart and spine.
More Stories About Suspected Fetal Macrosomia
Jamie's Story: I had several ultrasounds during my pregnancy because of GD. They were worried about macrosomia. Big babies run in my husband's family but I always felt like no one listened when I told them this. The last ultrasound I had was at 35 weeks, and they estimated the baby's weight to be 8 lbs, 5 oz...The doctor and midwife seemed concerned that she was going to turn out very large. We also found out she was a footling breech. I was going to have a scheduled c-section at 38.5 weeks because of this and their fear of how large she might get (as long as her lungs were mature enough).
My water broke spontaneously and I went into labor at 37.5 weeks. I went to the hospital and had the c-section and had a healthy 8 lb. 1.7 oz. baby girl. [Kmom note: They predicted the baby to be 8 lbs., 5 oz. at 35 weeks. Babies gain up to a half pound a week towards the end sometimes. By prediction, she should have weighed about 9 lbs. or more at 37 weeks, but she was just barely 8 lbs.] If the ultrasound estimate had been accurate, I think she should have been over 9 pounds when I had her. But obviously they were wrong. If I have another baby, I will take the estimates with a grain of salt.
Balek's Story: I measured large for dates through my pregnancy. It says "LGA" (Large for Gestational Age) all over my chart. Despite the fact that we had confirmed the dates at 14 weeks and that my mother had measured LGA all through both her pregnancies, my doc was worried about whether I could get a large baby through my pelvis. The first time I heard about this was around 41 weeks, when we did a NST. They estimated the baby at just over 9 lbs., plus or minus 1 lb.
My doc thought I would have a 10-pounder, and got worried about [shoulder] dystocia, despite the fact that another doc she consulted said she thought I had plenty of room for my baby. Long story short: At 42.5 weeks and an induced labor (with no pain meds), I had a c-section (probably due to an unresolved malposition, we think in hindsight). The baby weighed 8 lbs., 6 oz.
My new midwives' group says that 8 lbs. 6 oz is not big, especially for 42.5 weeks, and they don't think I'll have any trouble with a VBAC, even with a bigger baby. And I'm again measuring LGA; the women in my family just grow Olympic-sized pools for our normal-sized babies! [Kmom update: Balek had her 2nd baby vaginally (VBAC). This baby was 9 lbs. 5 oz. and was born very easily. So much for the first doc worrying about whether a large baby could 'get through' her pelvis!]
Stephanie's Second Story: My final u/s was at 36 weeks. This is when the u/s determined that the baby was around 9 pounds, 4 ounces. The technician told us that she takes measurements of his head and femur to determine the size. I was then advised by my doctor that it would be wise to schedule a c-section (she did give me the option of trying labor). We scheduled the c-section for the next week. My water broke [the day before]; I had a c-section at 8:33 that morning, and my little boy was born 10 pounds, 1 ounce and 20.5 inches long.
Denise K's Second Story: This was my first baby. I was diagnosed with GD early on and had frequent ultrasounds. In my 38th week the perinatologist looked at the baby and said that we'd probably have at least a 10 lb'er. When I was induced [a week later, or one week before the due date] and subsequently had my baby, he weighed 8 lbs 1 oz. He wasn't a TINY baby but he wasn't a 10 lb'er.
I think personally (and this is just my opinion) that simply because I am a big woman and had been diagnosed with GD, they expected my baby to be big, and the readings of the ultrasound would then follow suit. I don't know how often this particular doctor is "right" but in my case he was off [by 2 lbs.]. It WAS the perinatologist that did the u/s for me too, not a tech.
Mina's Story (summarized from her accounts): Doctors predicted a big baby and ordered extra ultrasounds to estimate the baby's size. The ultrasound she had the Monday before the baby was born estimated the baby at 9 lbs. The baby was born vaginally a few days later at 7 and a half pounds. Shows how reliable estimated fetal weight usually is! Off by nearly 2 pounds in this case.
Large Women and Ultrasounds
Although many larger women are anxious about their ultrasounds beforehand, most find the experience to be no big deal. However, as with any woman, ultrasounds should not be done for trivial reasons, and they should be done with respectful and caring attitude.
When making the appointment, you might want to inform the receptionist that you are a larger woman and would like someone experienced in doing ultrasounds on larger women. Be sure to bring your partner along for the ultrasound experience; it can be very amazing and intimate to "see" your baby like this. Don't overdo ultrasounds to get such emotional gratification, but if you do plan to have one, take the opportunity to enjoy "seeing" the baby together.
Large women may have more transvaginal ultrasounds than women of average size, especially early in the second trimester. If you are uncomfortable with the thought of a male technician for a transvaginal ultrasound, feel free to request a female tech. This is not unusual at all and should not be a problem. If you are unexpectedly scheduled with a male technician, be sure to request a female worker be present in the room with you. This should be standard practice, but sometimes you may need to request it. Don't hesitate to ask for whatever will make you more comfortable in this situation.
Often ultrasound machines in the doctor's office are less powerful and the ultrasound techs less trained than those found in a business that specializes in ultrasounds. Techs in ultrasound centers may also be more experienced with doing ultrasounds on women of size, and more adept at different techniques that can be used to help "visualize" things better if there are any difficulties because of size. So, if you have a choice, you may want to choose an ultrasound at a practice that specializes in ultrasounds and prenatal testing.
Remember to acknowledge to the tech that ultrasounds can sometimes be a bit harder with larger women, and that you appreciate that difficulty but are concerned about having a good experience. Request that they start with more gentle pressure at first and only increase the pressure as needed. If the pressure gets to be too uncomfortable, be sure to let the tech know and ask them to ease off a bit. If you are upfront and matter-of-fact about your concerns, most technicians will respond positively and work with you to make the experience more pleasant. If necessary, sometimes it helps to request a different technician if you have problems with one pressing too hard.
Although most women of size have no problem, it can sometimes be harder to get a clear image in a larger woman, especially if other factors such as an anterior placenta or oddly-positioned baby come into play. There are techniques that can help clarify an image in a woman of size, such as lifting the belly "apron," turning the woman on her side, putting the transducer in the woman's belly-button, or doing a transvaginal ultrasound.
However, the best defense is probably a good offense---schedule your ultrasound at a tertiary center that specializes in ultrasounds. They will have the most powerful equipment and most highly trained personnel, and will most likely be the most familiar with the "tricks of the trade" that can help get a clearer image in people of size. If in doubt, also schedule your ultrasound a little later in pregnancy, when it is easier to see images more clearly in women of size.
If there is a concern about the results of your ultrasound, always request another scan, preferably with a powerful machine and an extremely experienced tech or doctor. Often, waiting a few extra weeks to do a follow-up ultrasound can help clear up any unclear findings. If necessary, get yet another opinion from a perinatologist or ultrasound specialist, and be very cautious about taking drastic action based on only one or two ultrasounds. Remember the weaknesses of ultrasound testing as well as its strengths.
If a provider tells you that you will require multiple ultrasounds simply because of your size, this is a sign that your provider is probably not very size-friendly and may not have good clinical skills at ascertaining fetal position or growth. Although there can be special situations that might require extra ultrasounds in big moms, there is no need to do routine ultrasounds in women of size for tracking fetal growth or position.
As a big mom, be especially cautious about ultrasounds near the end of pregnancy to estimate fetal size. Estimated fetal weight is not very accurate in general, especially as babies get bigger. An ultrasound to estimate fetal size, although sometimes correct, is generally only slightly more accurate than tossing a coin in the air. Remember also that ACOG does not recommend early induction of labor if the baby is suspected to be big, and does not recommend elective cesarean unless the baby is extremely large (around 11 pounds or more).
Although big babies are at increased risk for shoulder dystocia and birth trauma, remember that most big babies ARE born vaginally and without problems. Avoiding things such as forceps, induction, and birthing on your back or in restricted positions can probably lower the risk for shoulder dystocia, and may be more sensible precautions than doing ultrasounds for fetal size. Each situation must be judged on its own merit, of course, but generally speaking, most research shows that interventions based on estimated fetal size are not beneficial and often end up doing more harm than good.
Unfortunately, early induction for suspected macrosomia is an extremely common intervention with women of size, and probably one reason the cesarean rate in big moms is so high. The first step to this is the seemingly innocent ultrasound for fetal size. Be VERY cautious about using the technology in this way, and strongly question any plan for early induction or elective cesarean based on estimated fetal weights.
If at any time, any doctor or ultrasound tech is less than respectful about your size, be sure to firmly let them know that you will not tolerate such treatment. If necessary, get another tech that is more size-friendly. An objective discussion by the tech of the challenges involved in doing an ultrasound on a larger person can be appropriate, but unkind remarks or put-downs are NEVER justified. How something is said is also as important as what is being said.
If you encounter prejudice, be firm but not emotional; forceful but not unpleasant. A polite but assertive approach tends to get the best results. Afterwards, feel free to rant and rave to safe people in a safe and understanding environment. Being calm and assertive gets more results in public but eventually it is important to vent all your negative feelings so they do not fester and create stress for the baby.
Follow up your complaint with a written letter expressing your concerns, and be sure to send copies not only to the doctor, but also to the radiology department head, the hospital, and the insurance company. Oftentimes this will get action. Even if it does not generate any reprimand or dismissal, you have raised awareness of the issue and stood up for yourself, and that alone is very important.
It's terrible that size prejudice is so prevalent in the medical community, but that doesn't mean that we have to tolerate it. Stand up for yourself, and stand up for your baby. You both deserve only respectful, loving vibes surrounding you during this vulnerable time, and that includes during any ultrasounds. No one should have to put up with biased treatment or cruel comments; don't stand for it. Remember that only through OUR action will it even be noticed, let alone stopped.
We must do this not only for ourselves, but for the women who follow after us, and for our unborn babies who will follow after that. Stand up to size bias HERE AND NOW, for the sake of ourselves and our children.
Ultrasound? Unsound. Beverley A. Lawrence Beech and Jean Robinson. London: Association for Improvements in the Maternity Services. 1994. Available from www.midwiferytoday.com.
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 During Pregnancy and Childbirth, Third Edition. Murray Enkin, et al. Oxford: Oxford University Press. 2000.
Excellent book describing evidence-based practices in obstetrics (which common practices are justified by research and which are not). Based on the Cochrane Collaboration of evidence-based medicine reviews. About shoulder dystocia, it states, "After delivery of the head, the shoulders rotate internally...Once rotation is complete, the shoulders are delivered one at a time to reduce the risk of perineal trauma...Difficulty with delivery of the shoulders is rare following spontaneous birth of the head. Delivery of the shoulders should not attempted until they have rotated into the anteroposterior axis."
Carrying A Little Extra: A Guide to Healthy Pregnancy For The Plus-Size Woman. Paula Bernstein, MD, PhD. With Marlene Clark, RD, and Netty Levine, MS, RD. New York: Berkley Books. 2003.
Well-intentioned but disappointing book about pregnancy in obese women. Pays lip service only to the idea that plus-sized women can have healthy pregnancies and babies, but spends most of the book strongly emphasizing things that can go wrong. Only stories of complications and problems are presented, and only cesarean birth stories are told. Normal pregnancy and birth in women of size are almost completely ignored. The first half of the book is a summary of the possible risks of pregnancy in larger women, written by an OB/GYN who is also a mid-sized woman herself. The second half of the book is written by two registered dieticians who give information on about nutrition for larger women in pregnancy. Although carb-heavy, the guidelines are generally sensible, but the tone is very patronizing and condescending, as if women of size can't be trusted to eat properly on their own and must be constantly lectured to avoid them gaining too much weight in pregnancy. Although all the the authors certainly mean well, their unconscious size-phobic attitudes come through clearly anyhow.
Websites About Ultrasound
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 www.ob-ultrasound.net.
Ultrasounds in Women of Size
Wolfe, HM et al. Maternal Obesity: A Potential Source of Error in Sonographic Prenatal Diagnosis. Obstetrics and Gynecology. September 1990. 76(3 pt 1):339-42.
Above the 90th percentile, visualization fell by an average of 14.5%. "Reduction in visualization was most marked for the fetal heart, umbilical cord, and spine."
Rosenberg, JC et al. Transumbilical Placement of the Vaginal Probe in Obese Pregnant Women. Obstet Gynecol. January 1995. 85(1):132-4. [from abstract]
Reports their experience in using transvaginal probes in the umbilicus (belly button) of obese women in order to help improve resolution. The subjects were 25 consecutive obese women with "unsatisfactory fetal imaging by the standard transabdominal approach." In most cases, the incomplete area was satisfactory imaging of the fetal heart (19/25 cases).
Subjects had their bellybuttons filled with ultrasound transmission gel, and then a transvaginal probe was inserted into the umbilicus. This approach improved resolution and resulted in satisfactory cardiac examination in 18 of the 19 fetal heart cases. Authors note that of the 25 cases, "a complete fetal survey was accomplished in 96%" (presumably 24/25 cases).
McCoy, MC et al. Transumbilical use of the endovaginal probe. Am J Perinatol. October 1996. 13(7):395-7. [from abstract]
Also reports the success of using the vaginal probe transducer in a woman's belly-button in order to improve fetal imaging. In this study, this technique helped 27/31 patients achieve an optimal ultrasound exam. "The procedure is most useful in obese women and those with prior abdominal surgery."
Field, NT et al. The Effect of Maternal Obesity on the Accuracy of Fetal Weight Estimation. Obstetrics and Gynecology. July 1995. 86(1):102-7.
Over a year, 998 pregnancies underwent both clinical and sonographic estimation of fetal size, which was then compared with actual fetal size. Patients were stratified into 4 BMI groups: underweight (<19.8 BMI), normal weight (19.8-26 BMI), overweight (26-29 BMI) and obese (>29).
There was no increase in the magnitude of error with increasing maternal obesity. Regardless of maternal size, 42-48% (not quite half) of weight predictions were within 5% of actual birth weight, and about 2/3 were within 10% of actual birth weight, although remember that this can represent a range of up to a pound. This study also found that clinical estimations were just as accurate in women of size as sonographic ones.
Discusses that while ultrasound accuracy in detecting birth defects can be affected by maternal fatness, accuracy is not affected for fetal weight estimation. This is "mostly a consequence of abnormalities in ultrasound attenuation...the loss of strength of the ultrasound waves as they propogate through tissue." High density structures like bones reflect u/s waves well, despite maternal fatness, and fetal weight estimates are based mostly on bony landmarks like biparietal diameter and femur length. "Thus it is not surprising that obesity had no adverse influence of the accuracy of fetal weight estimations because the bony structures and fetal landmarks used in equations for fetal weight calculations are distinct sonographically and require little or no detailed resolution."
"In no patient did obesity preclude the estimation of fetal weight by either clinical or sonographic examination...Increasing maternal obesity does not alter or decrease the accuracy of either clinical of sonographic fetal weight estimates...Regardless of maternal size, the limitations of determining fetal weight either clinically or sonographically are essentially the same"
Shamley, KT and Landon, MB. Accuracy and Modifying Factors for Ultrasonographic Determination of Fetal Weight at Term. Obstetrics and Gynecology. December 1994. 84(6):926-30.
223 women near term underwent ultrasound examination, and the accuracy of four different fetal weight estimation equations were tested. The Hadlock (abdominal circumference plus femur length) and Shepherd (abdominal circumference plus biparietal diameter) equations did best but because the Hadlock equation does not require a biparietal diameter (which was difficult to measure in about 2/3 of the women studied), the authors recommended it over the other equations.
70-79% of fetal weight predictions were within 10% of actual birth weight, a better accuracy rate than in most studies, BUT most of the accuracy was for babies of average size. Ultrasound for estimating fetal size was much better at ruling out macrosomia than for diagnosing it. Of note, maternal weight did NOT affect predictive accuracy.
Farrell, T et al. The Effect of Body Mass Index on Three Methods of Fetal Weight Estimation. BJOG. June 2002. 109(6):651-7.
96 women being induced had the size of their fetuses estimated by 3 different methods: clinical palpation (hands-on estimating of size based on fundal height etc.), maternal estimation (mother guesses the baby's size), and ultrasound fetal weight estimation. All did equally well, overall. In the whole group, 61% of clinical estimates were right within 10% of true birth weight, 63% of maternal estimations were in that range, and 72% of ultrasounds were within that range. (Thus ultrasound did slightly better.) In the group with a Body Mass Index <32, 67% had an accurate range of birth weight by clinical estimation, 63% by maternal estimation, and 74% by ultrasound estimation. In the obese group (BMI>32), accuracy rates dropped particularly in the clinical estimation range (55%), the maternal estimates range were about the same (64%), and the ultrasound estimation was slightly less accurate as well (64%) but the authors felt the difference was "of little clinical significance."
Of note in this study, clinical estimations in the obese group were within 10% of the baby's birth weight only slightly more than half of the time. The authors noted a strong tendency to overestimate the true fetal weight of high BMI women by clinical estimation. This probably reflects the typical bias of doctors assuming that a large woman will automatically have a larger baby, and that a greater fundal height in large women likely indicates a macrosomic baby.
One possible error in this study is that clinical estimation of weights was done by only one person; a broader spectrum of clinicians might have a different (and hopefully better!) result. In most studies, clinical estimation and maternal estimation is just as accurate as ultrasound estimation. In this study, ultrasound estimation was slightly more accurate than clinical or maternal estimation. However, even so, only 2/3 to 3/4 of estimations were even within 10% of fetal weight, and that still means estimates can be off by almost a pound. The authors conclude, "Errors in weight estimation of [plus or minus] 20% are possible and must be borne in mind when decisions regarding obstetric management are formulated."
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:
- "The diagnosis of fetal macrosomia is imprecise. For suspected fetal macrosomia, the accuracy of estimated fetal weight using ultrasound biometry is no better than that obtained with clinical palpation (Leopold's maneuvers)."
- "Suspected fetal macrosomia is not an indication for induction of labor, because induction does not improve maternal or fetal outcomes."
- "Labor and vaginal delivery are not contraindicated for women with estimated fetal weights up to 5000 g [Kmom note: about 11 lbs.] in the absence of maternal diabetes."
- "With an estimated fetal weight greater than 4500 g [Kmom note: about 9 lbs. 14 oz.], a prolonged second stage of labor or arrest of descent in the second stage is an indication for cesarean delivery."
- "Although the diagnosis of fetal macrosomia is imprecise, prophylactic cesarean delivery may be considered for suspected fetal macrosomia with estimated fetal weights greater than 5000g in women without diabetes and greater than 4500g in women with diabetes."
- "Suspected fetal macrosomia is not a contraindication to attempted vaginal birth after a previous cesarean delivery."
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 morbidity...it 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.
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
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.
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.
Shoulder Dystocia Research
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
Bruner, JP et al. All-Fours
Maneuver for Reducing Shoulder Dystocia During Labor.
Journal of Reproductive Medicine. May
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.
Nixon SA et al. Outcomes of macrosomic infants in a nurse-midwifery service. J Nurse Midwifery. Jul-Aug, 1998. 43(4):280-6.
This study compared outcomes of infants of average birth weight with outcomes of large infants in a nurse-midwifery service. Shoulder dystocia occurred more often in large infants. The authors note, "A trend for fewer occurrences of shoulder dystocia in the side-lying birth position was observed."
Studied whether there is a risk profile for predicting or preventing shoulder dystocia, and which obstetric maneuvers for SD reduce permanent injury. 1.4% of vaginal deliveries had shoulder dystocia. Birth weight was the most significant risk factor for shoulder dystocia. Prior large infant was also a risk factor. Diabetes and midforceps delivery were significant only when there was a large baby. Obesity was NOT a risk factor for shoulder dystocia. Neither was postdates pregnancy, use of oxytocin, low forceps, and multiparity. The authors conclude, "This study clearly indicates that most of the traditional risk factors for shoulder dystocia have no predictive value, shoulder dystocia itself is an unpredictable event, and infants at risk for permanent injury are virtually impossible to predict. In addition, no delivery method in shoulder dystocia was superior to another with respect to injury. Thus no protocol should serve to substitute for clinical judgment."
Lewis, DF. Can Shoulder Dystocia Be Predicted? Preconceptive and Prenatal Factors. The Journal of Reproductive Medicine. August 1998. 43(8):654-8.
Studied fetuses who experienced shoulder dystocia and a group of controls. Found macrosomia to be higher in the group with shoulder dystocia (35% vs. 5%). Previous shoulder dystocia, concurrent diabetes, prior delivery of a macrosomic fetus, and excessive weight gain during pregnancy were associated with shoulder dystocia. Factors NOT associated with shoulder dystocia in this study included obesity, multiparity, history of diabetes, short stature, postdatism, and advanced maternal age.
Workshop, "Shoulder Dystocia Re-Examined," presented by Gail Hart, Midwife, at the Midwifery Today Conference, March 2001.
An excellent workshop, Hart presented numerous obstetrics, nursing, and midwifery manual quotations suggesting that the birth of the shoulders NOT BE HURRIED but that it is very important to wait for the shoulders to rotate first.
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