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‘Keepsake’ Ultrasounds Aren’t Dangerous

For pregnant women (and their partners), prenatal ultrasounds can be awe-inspiring. It’s undeniably neat to actually see what the baby looks like before he or she emerges, and the resulting pictures make excellent decorations for the refrigerator.

Most women will have two or three medically recommended ultrasounds during pregnancy. But some women and their partners would like more time watching their growing babies, and more pictures. To serve these consumers, a cottage industry of “recreational” ultrasound studios has emerged, offering “keepsake ultrasounds” — 3-D pictures of the fetus, long video recordings, etc. Ultrasound sessions at these providers can last up to an hour.

Recently, the Food and Drug Administration issued stringent warnings against use of these providers. It “strongly discourages” these services on the theory that ultrasound heats tissues and could cause fetal damage. Although the agency notes that such ultrasounds might promote “bonding” between mother and baby, the lack of medical benefit means (in its view) that these extra procedures should be avoided.

The FDA warning is unusual in the sense that it explicitly says there is no affirmative medical reason to think keepsake ultrasounds are dangerous. The disconnect between this observation and the strength of the recommendation makes a good case for looking at the underlying evidence. In fact, there is little or no clear evidence behind the recommendation.

The first thing to say is that there is no evidence of any type on the use of recreational ultrasounds. There are no studies of birth outcomes for mothers who did or did not have these procedures performed. Basically, we know nothing directly.

The closest the medical literature has to offer are studies of medical ultrasounds — that is, studies that compare women who had more or fewer ultrasounds performed by their doctors during pregnancy. But there aren’t many studies of this either. The basic barrier is simple: Usually, women who have multiple ultrasounds are having them for a particular reason.

Women with healthy, low-risk, uncomplicated pregnancies typically have two or three ultrasounds. Women with pregnancy complications — twin pregnancies, pregnancies with fetal growth restriction, etc. — tend to have more ultrasounds. Comparing these two groups and attributing differences in infant outcomes to differences in ultrasounds is obviously problematic. It’s so obviously problematic that it’s virtually never done.

This leaves us with a small number of studies that randomly allocate women either to normal ultrasound follow-ups or to more frequent ultrasounds during pregnancy, and then compare their fetuses. Among the largest of these is a study of almost 3,000 women in Australia that randomly allocated half the women to the standard single-ultrasound treatment and the other half to a series of five ultrasounds over the second half of their pregnancies.

This study found no difference in virtually all the outcomes it considered: APGAR score (a measure of health at birth), average birth weight, need for interventions with the newborn, time spent in the NICU, neonatal death, gestational age at birth, etc. One outcome, the chance of a very small baby (below either the 10th percentile or the third percentile in birth weight), was slightly more common in the frequent ultrasound group. The number of infants in this category is very small and, as the authors note, it is possible this outcome occurred by chance.

The study followed participants as the children aged and continued to find no differences between the two groups. By age 1, the differences in size had been erased, and there were no difference across groups in speech and language development, neurological or behavioral issues.

The null effect of ultrasounds on infant and child outcomes is generally echoed in other work. A 2010 Cochrane review (a meta-analysis of randomized trials) concluded there were no long-term negative effects of ultrasounds before 24 weeks of pregnancy on fetal outcomes or child development. A second review showed the same null effects of ultrasounds conducted later in pregnancy.

This evidence suggests that there is absolutely no reason to avoid ultrasounds as administered during prenatal care. There has been some reluctance to extend this conclusion to recreational ultrasounds because of concerns they may last longer or use different ultrasound power settings. But, again, there is no evidence on this either way.

A significant part of the FDA’s argument is there is no medical benefit to these ultrasounds. The only benefit is that the expectant parent might enjoy them. This is true, although it is perhaps worth noting that there are no medical benefits to many behaviors in pregnancy that are considered acceptable. There is no medical reason for sex when you’re pregnant other than enjoyment, and it’s generally considered fine to engage in.

In my view, the strongest argument in favor of the FDA warning relates to misuse of the information contained in these ultrasounds. An ultrasound is not exactly high-def TV, and doctors (or doctor-employed ultrasound technicians) are likely to be much better at interpreting the images than a technician who performs them for parents’ entertainment. A poorly trained technician might see problems with the fetus when they are not there, causing unnecessary worry, or might fail to see problems that are there. There isn’t much evidence on the magnitude of either of these concerns beyond anecdote, making it difficult to evaluate their import.

Oddly, the strongest argument against issuing the FDA’s warning may also relate to misuse of information. It is entirely possible that pregnant women will react to the warning by concluding that routine diagnostic ultrasounds carry some risk. After all, it is hard to avoid this conclusion: The FDA says some version of ultrasound is dangerous, so how do you square this with the view that the ultrasounds your doctor recommends are fine?

This conclusion would be dangerous. Diagnostic ultrasound is enormously useful in obstetrics, for everything from evaluating fetal position to guiding a needle in amniocentesis to monitoring growth restriction and umbilical blood flow. A warning that causes women to balk at standard ultrasound monitoring would be a very bad one.

Emily Oster is an associate professor of economics at Brown University and the author of “Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong — and What You Really Need to Know.”