Ultrasound - Wikipedia


obstetric ultrasound dating accuracy

HCG Levels for normal Pregnancy. Magnesium sulfate administration is recommended to decrease the risk of cerebral palsy if your patient is at risk of preterm delivery before 32 weeks A course of antenatal corticosteroids is recommended if your patient is between 24 and 34 weeks of gestation and is at risk of preterm delivery within 7 days. The authors finished by stating, "We observed an association between sonographic estimation of fetal weight at term and the management of labor and delivery.

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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! 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! Data from meta-analyses have shown that cervical shortening on transvaginal ultrasound examination identifies twin pregnancies that are at high risk for preterm birth. Having a sense of humor about it makes it easier. 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.

ISUOG's World Congress is the main annual scientific meeting for clinicians who use or research ultrasound in obstetrics and gynecology. Our Pre-Congress Courses offer the chance for a day of specialised teaching on a specific subject.

This Virtual Issue on Cesarean scar pregnancy CSP and abnormal invasion of the placenta AIP brings together a series of original research articles, systematic reviews and editorial pieces which highlight the use of prenatal imaging in detecting CSP and AIP, as well as the role that early diagnosis can play in reducing the morbidity associated with these conditions.

New research highlights a more accurate way to screen for preeclampsia in pregnant women than currently recommended methods. The chairs for this unmissable event are G. Condous Australia and G. Yeo Singapore , and our confirmed faculty already includes many prominent experts in obstetrics and gynecology, with more speakers to be confirmed.

ISUOG Outreach provides intensive hands-on training in ultrasound supported by essential theoretical knowledge, in underserved regions of the world. See our Outreach page for a list of current training projects.

A Practical Approach , in its Outreach projects. Renew your membership before the end for uninterrupted access to your member benefits. Do what seems best in your circumstances. As noted, it can be harder to "see" everything clearly when doing an ultrasound in a woman of size. 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. 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.

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: 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.

If they need to switch modes, then it's no big deal. 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. 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. 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.

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. 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. 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.

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.

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.

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.

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. 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 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 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.

Being our first pregnancy, we decided the hospital must be right and we continued with our near perfect pregnancy. 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. 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. 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 rightshe was 3 weeks early at birth [Kmom note: More like a month! Because my husband is 6 ft. 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.

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. 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, "S ome of the yardsticks doctors traditionally use 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.

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. 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.

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! 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. 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. 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: 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 g to be macrosomic, the American College of Obstetricians and Gynecologists considers g 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 ultrasoundan 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.

For example, Pollack et al. 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.

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.

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. Even when inducing early did not increase the cesarean rate Gonen , 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 , Jazayeri , Nesbitt 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.

Weeks studied the effect of the label of predicted macrosomia. The authors concluded, " Ultrasonography and labor induction for patients at risk for fetal macrosomia should be discouraged. Parry also found that the mere prediction of macrosomia raised the cesarean rate. Again, the babies were the same size, but the prediction of macrosomia was enough to nearly double the cesarean rate. Another study, Levine et al. 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, , reviewed the evidence in the medical literature from and concluded: Sonographic estimates are no more accurate than clinical estimates of fetal weight.

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. 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.

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.

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 , Field , Farrell 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. Our study suggests that the effect of maternal BMI on 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. Mortimer Rosen, writing in The Cesarean Myth , states,. 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, did NOT find the pelvic outlet dimensions of fat women to be significantly affected. The common assumption can no longer be maintained, that adiposity necessarily causes soft tissue [dystocia] due to larger fat compartments within the small pelvis. If the "padded pelvis" theory were true, then you'd never see a or 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 lbs. 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 shows that this is not true. 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.

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 , Lewis 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. 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.

However, even in this group, research has found interventions to be questionable below a fetal weight of about 10 lbs. 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 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.

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. 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.

Sandmire, , 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.

For this reason, intervention--either cesarean delivery or early induction--does not appear to be indicated for fetuses with macrosomia diagnosed by ultrasound.

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.

They estimated my son to be 8. I had an ultrasound around The result the technician gave was "about 7. He then said that he really thought the baby was more like 8. 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. 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. 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. Well, another week went by, still no labor, so underwent induction with laminaria insertion the night before Never dilated more than 3 cm after But, my wonderful darling daughter was only 8 lbs. 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.

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. Of course with a plus or minus of a pound. 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.

She, [an ultrasound tech] who does this every day, said, "I have no idea. 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. 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. That tech, at a completely different facility than the first two, gave me an estimate of 8 lbs. 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. He had a 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! 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. 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. I'm ready to do it again. 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.

Fundal pressure pushing on the top of the uterus also increases the risk for problems Gross Induced labor also increases the rate of shoulder dystocia in some studies Combs , Jazayeri , Nesbitt , 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 , Bruner 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 state: It would seem that prevention of morbidity would be best accomplished by proper and immediate management of shoulder dystocia once it occurs.

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 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.

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.

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. 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.

Iamges: obstetric ultrasound dating accuracy

obstetric ultrasound dating accuracy

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. They estimated my son to be 8. With rare exception, if a first-trimester ultrasound examination was performed, especially one consistent with LMP dating, gestational age should not be adjusted based on a second-trimester ultrasound examination.

obstetric ultrasound dating accuracy

This is why the latest clinical management guidelines for macrosomia from the American College of Obstetricians and Gynecologists state:

obstetric ultrasound dating accuracy

A 1st trimester series should include the following minimum images. Thus, unless it is proven that the presence of obesity should obstetric ultrasound dating accuracy these recommendations, expectant management should be the course of action for nondiabetic obese women with a suspected big baby. Only after 53 days is the fetal rump the most caudal portion of the fetus. Borel Was Starting Medical School. It is common for a twin pregnancy to undergo spontaneous reduction in the first trimester.