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Comment and Controversy

Estimating fetal weight is difficult in obese women

April 2009 · Vol. 21, No. 04
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I enjoyed the articles on obesity in pregnancy and would like to add one point. Ultrasonographic imaging in the obese gravida is often poor. I suggest that the anatomic survey, usually recommended for 18 to 20 weeks of gestation, be postponed to 22 to 24 weeks in this population. True, you may miss the opportunity to assess the nuchal fold, but that is not so important if you also perform first-trimester genetic screening.

The new transducer being advertised by Philips for their iU22 ultrasound system may make this suggestion less important (I don’t know—I have not used it). In time, it is likely that all machines will do a better job of imaging in the obese patient, but there is, for now, an enormous difference in the quality of imaging between thin and obese patients.

Because of this problem, there is a great likelihood that something will be missed in the obese gravida. I also tend to have less confidence in fetal biometry in this population, particularly in the third trimester.

Joseph A. Worrall, MD, RDMS
Fairbanks, Alaska

How to reduce wound dehiscence in obese gravidas

Congratulations on the excellent articles on obesity in pregnancy. When it comes to closing the abdominal wound in extremely obese women who require cesarean delivery, I suggest retention sutures of #5 (or #4) Mersilene, which I have used for more than 40 years.

I close the parietal peritoneum, then insert the sutures (without tying them) through the rectus abdominis, rectus fascia, subcutaneous fat, and skin. I then close each anatomic layer. After closing the skin, I tie each retention suture moderately tightly and apply a sterile dressing. I remove the staples on postop day 5 or 6 and the retention sutures 48 hours later.

I have never encountered wound dehiscence using this technique. (By the way, until 1982, I had to use heavy thread or nylon sutures.)

Peter M. Zablotsky, MD
Queens, NY

Look for vitamin D deficiency

Another deficiency to screen for in the obese gravida is vitamin D. Measurement of 25-OH vitamin D should be routine in this at-risk population.

John Lewis, MD
Waterbury, Conn

Dr. Phillips and Dr. Henderson respond:

Dr. Worrall makes a good point. The fetal anomaly screen can be challenging to perform in the obese patient; waiting until after 20 weeks’ gestation can help improve visualization. In some cases, however, adequate visualization may never be achieved, and some anatomy may be incompletely evaluated.

In a study in 1990, Wolfe and colleagues found complete ultrasonographic (US) visualization to be 14.5% lower in women who had a body mass index above 36.1 Some have used transumbilical US (using a transvaginal probe) in an attempt to improve visualization.

Dr. Zablotsky’s pearl is useful. We like to use a long-lasting absorbable monofilament suture, such as PDS, on the fascia for added support.

Dr. Lewis is correct that vitamin D is an important screen, especially in women who are vegetarian or who have minimal sun exposure.


1. Wolfe HM, Sokol RJ, Martier SM, Zador IE. Maternal obesity: a potential source of error in sonographic prenatal diagnosis. Obstet Gynecol. 1990;76:339-343.

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