An Attempt to Investigate Late Pregnancy Ultrasound

I’ve been researching this topic for several hours throughout the day now. I’ve learned a great deal:

1. It is no wonder doctors may not have time to stay up on the latest research.
2. Much research has to be done to prove things don’t make a difference.
3. It seems more questions are created than answered by much research.
4. It is very tough to find answers to simple questions.
5. Ultrasound and sonogram appear to be synonymous in the literature.

I’ve spent my time at sites that have impeccable reputations: Journal of the American Medical Association (http://jama.ama-assn.org/), The Lancet (www.thelancet.com ), The American Journal of Obstetrics and Gynecology (http://www.ajog.org/), The Cochrane Library (http://www.moh.govt.nz/cochranelibrary), and Midwifery Today (http://www.midwiferytoday.com). In addition, I’ve only used studies that were from 1994 or later. If you would like the full abstract and publication information from the studies I’m presenting, please email me at jennie@windyhouse.net. I’ve not included that information in this post for the sake of your time and my sanity.

Here’s what I didn’t find: What is the +/- discrepancy in the birth weight of babies who’ve had an ultrasound in the third trimester? What is the accuracy of palpation (using your hands) to determine birth weight? (Why use the machine if the hands do just as good a job?)

Here’s what I did find:

This article first appeared in Midwifery Today Issue 51, Autumn 1999
(Note from Jennie: I am giving you the whole of this section from Midwifery Today not because I want to place more emphasis on it, but because it didn’t have a succinct summary as the other abstracts do.)

“One of the promises held out by antenatal scanning is that obstetricians will be able to identify the baby with problems and do something to help it. A German study from Wiesbaden hospital (Jahn et al., 1998) found that out of 2,378 pregnancies only fifty-eight of 183 growth retarded babies were diagnosed before birth. Forty-five fetuses were wrongly diagnosed as being growth retarded when they were not. Only twenty-eight of the seventy-two severely growth-retarded babies were detected before birth despite the mothers having an average of 4.7 scans.

The babies diagnosed as small were much more likely to be delivered by caesarean - 44.3 percent compared with 17.4 percent for babies who were not small for dates. If the baby actually had intrauterine growth retardation (IUGR) the section rate varied hugely according to whether it was diagnosed before birth (74.1 percent sectioned) or not (30.4 percent).

So what difference did diagnosis make to the outcome for the baby? Pre-term delivery was five times more frequent in those whose IUGR was diagnosed before birth than those who were not. The average diagnosed pregnancy was two to three weeks shorter than the undiagnosed one. The admission rate to intensive care was three times higher for the diagnosed babies.”

From the American Journal of Obstetrics & Gynecology in 2003.

Conclusion: Term birth weight estimates that use ultrasonography are generally no more accurate than predictions that are based solely on quantitative assessment of maternal and pregnancy-specific characteristics. (Jennie explains: Meaning, knowing mother’s weight gain, fundal height, gestational diabetes status, and family history)


From the American Journal of Obstetrics & Gynecology in 1994.

CONCLUSIONS: With either the single or multiple examination approach birth weight percentile estimates were within 10% of the actual birth weight percentile approximately 50% of the time. Multiple ultrasonographic examinations provided little improvement in prediction of birth weight compared with a single observation. Multiple measurements of the abdominal circumference percentile may provide improved accuracy in identifying large for gestational age and small for gestational age fetuses. (Jennie notes: This was a study of only 263 patients, but still fascinating.)

From the Journal of American Medicine in 1996.

CONCLUSIONS: For the 97% of pregnant women who are not diabetic, a policy of elective cesarean delivery for ultrasonographically diagnosed fetal macrosomia is medically and economically unsound. In pregnancies complicated by diabetes, such a policy appears to be more tenable, although the merits of such an approach are debatable. (Jennie notes: This was a review of the literature looking at over 6,000 women.)


And here’s one last anecdotal piece of information. We had an ultrasound with our first child on the day she was born; several actually. This was done to confirm that she was a footling breech, and to confirm how she was handling attempts at external version. The first ultrasound which was done, which was a full-length, diagnostic ultrasound, indicated that she would be around 6 lbs, 13 ozs. Our midwife, through palpation, estimated her birth weight at 7 lbs. Birth weight of first child: 7 lbs. 1 oz.