Large Abdominal Circumference?

Sherri Parker

Large Abdominal Circumference?
Dear Henci,

The last time I was pregnant and this worried, I wrote to you and you were enormously helpful.  Thank you so much.  My last childbirth was completely natural (except for the hospital setting) and 8lbs 2oz.  There was a bit of "shoulder stickiness", but my doula (who is actually a homebirth midwife) told me she believed that was more due to the doctor pulling on the baby than any sort of baby-pelvis issue.

This time I am being told that a c-section is recommended for me (I am a VBAC seeker - this would be my 3rd VBAC) because at 37 weeks my baby's ac is measuring 3-4 weeks ahead.  I am well aware of the nonsense of "big baby" c-sections, but this one is a new spin and the fear of shoulder dystocia is getting to me.  The perinatologist who measured me and made the recommendation is a very c-section happy fellow, who basically made it sound like I had no choice in the matter.  My OB is following his advice (somewhat) and wants me to sign an AMA this Friday (39 weeks) if I don't consent to surgery.  I am very scared.

I don't know if it makes a difference, but earlier scans were showing he had "symmetry" and thus the abdomen was not out of proportion to the rest of the body like it supposedly is now.
Basically I am asking you if you've heard of this "c-section for large abdominal circumference" thing, that seems to be a new thing, and how much science do you think is really behind it?

Thank you ever so much for your time and caring,

Henci Goer

RE: Large Abdominal Circumference?
(in response to Sherri Parker)

So as I read your analysis of the situation, you have the recommendation of a perinatologist whose judgment you can't trust because he is "c-section happy" that you should return to surgical delivery after two VBACs because he thinks the baby is getting too big, abdominal circumference being one of the ways of estimating fetal size. Heightening your concern is that the shoulders hung up a bit with the last baby; however, a midwife whose judgment you do trust told you that was because of the ob's management at the delivery, not because of any inherent problem between your pelvis and your baby's size.


As for the research, here is an excerpt from my book, Optimal Care in Childbirth: The Case for a Physiologic Approach:


A systematic review of studies estimating fetal weight (51 using formulas, 12 using fetal abdominal circumference) reported only modest to moderate ability using either strategy to rule macrosomia [estimated birth weight more than 4000 g or 8 lb 13 oz] in or out. The authors conclude: "The poor accuracy of ultrasound suggests that relying on ultrasound findings can lead to . . . an increase in interventions unnecessarily . . . when macrosomia is incorrectly ruled in by ultrasound scanning. . . . Over-reliance on them to guide practice should be avoided" (p. 1465).


Coomarasamy A, Connock M, Thornton J, et al. Accuracy of ultrasound biometry in the prediction of macrosomia: a systematic
quantitative review. BJOG 2005;112(11):1461-6.


In addition, having a prior VBAC greatly reduces the likelihood of having a problem with the scar in a subsequent VBAC labor as well as having a subsequent VBAC labor end in a cesarean. I have seven studies reporting VBAC rates of 90-97% with prior VBAC.  


If this summary of your analysis and the research information doesn't help you decide what to do, I recommend asking around to see who is a VBAC friendly doc in your community and getting a second opinion. This should be worth it even if you have to go outside your insurance network and pay out of pocket for the consultation. In fact, it may be worth it to switch doctors. Studies consistently find that the doctor's beliefs about whether the baby is too big for the woman to birth heavily influence judgment: when doctors suspect the baby is going to be big based on ultrasound prediction, the woman is much more likely to end up with a cesarean than if the baby really is big, but the doctor didn't suspect it.  Also, you already know that the ob who attended your last birth may not know how to assist properly at the birth of a good-sized baby. Speaking of which, the best way to get a baby out whose shoulders hang up is to turn to hands-and-knees or plan to give birth on hands-and-knees when a big baby is expected: Bruner JP, Drummond SB, Meenan AL, et al. All-fours maneuver for reducing shoulder dystocia during labor. J Reprod Med 1998;43(5):439-43.

I'd love to hear what you decide and how everything goes for you.


~ Henci



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