The Risks & Benefits of Ultrasounds

Ultrasounds have long been suspected of playing a role in autism, partly because their use has expanded dramatically over the same time period in which autism rates have spiked. Animal studies have also raised concerns, with researchers finding that ultrasounds can slightly raise the temperature of fetal tissues and interfere with brain development in mice. But it is far from clear that the same thing occurs in humans in real-world scenarios, or whether such effects could contribute to autism.

On the contrary, the human studies so far indicate that routine ultrasounds do not raise the risk of autism. In a 2018 study published in the prestigious journal JAMA Pediatrics, researchers found that, on average, children with autism had actually been exposed to fewer ultrasounds and ultrasounds of shorter duration.[i]

Dr. Sara Webb, an Associate Professor of Psychiatry at the University of Washington, who was not involved with the study, commented that “at this time, there is no evidence that ultrasound is a primary contributor to poor developmental outcomes when delivered within medical guidelines.” Several prior studies also failed to find a connection between ultrasound and increased risk of autism.[ii]

Yet Dr. Webb has commented that this body of research only means that ultrasounds are not a sufficient cause of autism on their own—it is still possible that ultrasounds have a negative effect in children who have a unique vulnerability.[iii] This question over how ultrasounds may interact with genetics is an issue flagged by Webb’s own research.

In 2017, Webb found that children with a specific genetic predisposition to autism who received ultrasounds during early pregnancy had more severe autistic symptoms than the children not exposed to ultrasound.[iv] This link seemed to be limited to scans performed in the first trimester; there was no association between severity of autism and the number of scans in the second or third trimester.

Webb notes that her findings support the FDA’s recommendation that ultrasounds should only be performed when medically necessary. “It’s worthwhile to consider why a first-trimester ultrasound is being done. The pictures do provide some bonding [between the parents and their child], but if it is not medically necessary, you should wait until later in the pregnancy,” she says.

The American College of Obstetricians and Gynecologists (ACOG) also advises that ultrasounds should only be performed for valid medical reasons. Their recent committee opinion states that ultrasounds “should be used prudently and only when use is expected to answer a relevant clinical question or otherwise provide medical benefit to the patient.”[v]

When exactly an ultrasound will provide medical benefit remains a murky issue. Large-scale reviews have failed to demonstrate much benefit to any routine ultrasound screenings.[vi] For example, a recent review analyzed a dozen prior studies involving almost 35,000 women who were randomly selected to ultrasound screening or a control group. The review concluded that:

Existing evidence shows that routine ultrasound, after 24 weeks’ gestation, in low-risk or unselected women does not provide any benefit for the mother or her baby . . . Babies’ birth weight, condition at birth, interventions such as resuscitation, and admission to special care were similar between groups. Infant survival, with or without congenital abnormalities, was no different with and without routine ultrasound screening in late pregnancy.[vii]

A review on ultrasounds earlier in pregnancy reached similar conclusions.[viii] It is hard to reconcile this bird’s-eye view with the fact that ultrasounds can sometimes provide useful information in individual cases. An ultrasound may, for example, find a rare anatomic problem that can be corrected with surgery, either in utero or immediately after birth.

Regardless of what the studies say, it is hard to deny that more information is better when it comes to the health of your baby. The ACOG therefore recommends “at least one” ultrasound for low-risk pregnancies, typically at 18 to 22 weeks. In many countries, the standard practice is to perform one ultrasound at approximately 12 weeks and another at approximately 20 weeks, in order to check that the baby is developing normally.

Beyond these standard milestones, the value of performing additional ultrasounds for low-risk pregnancies is questionable, and different doctors take different approaches. During the third trimester, there may be good reason to perform one or two additional scans to ensure the baby is growing at the proper rate. If growth slows dramatically (as a result of problems with the placenta, for example), doctors may consider inducing labor early. In rare cases, this can reduce the chance of stillbirth.[ix] For this reason, experts typically recommend an ultrasound to check for growth restriction once or twice during the third trimester, often at around 32 to 36 weeks.

The total number of ultrasounds considered “medically useful” is therefore typically around three, with scans performed at approximately 12 weeks, 20 weeks, and 32 to 36 weeks. Some doctors, however, choose to perform an ultrasound at every checkup, throughout the pregnancy. This is unlikely to be harmful, but there is no evidence that it provides any benefit for the mother or baby. It is also at odds with the official recommendations. The ACOG’s official position on this issue states:

Currently, there is no evidence that ultrasound is harmful to a developing fetus. No links have been found between ultrasound and birth defects, childhood cancer, or developmental problems later in life. However, it is possible that effects could be identified in the future. For this reason, it is recommended that ultrasound exams be performed only for medical reasons by qualified health care professionals. Casual use of ultrasound during pregnancy should be avoided. [x]

Although the research to date suggests that the chance of ultrasounds causing any harm is extremely low, there is still a risk/benefit analysis to be made. As the FDA notes, “While ultrasound is generally considered to be safe with very low risks, the risks may increase with unnecessary prolonged exposure to ultrasound energy, or when untrained users operate the device.”[xi]

If an ultrasound will not give any useful medical information, then arguably there is no justification for taking any risk at all. The counterargument to this point is that regular ultrasounds can help relieve anxiety for many expectant mothers, and this is a benefit in and of itself.

In some cases, the reassurance from regular ultrasounds could indeed outweigh the incredibly small risk that these tests are somehow harmful in ways that are not yet understood. This is a personal decision to be made, based on how much you personally gain from seeing your growing baby on the ultrasound screen.

The most prudent approach is to follow the official recommendations that ultrasounds should only be performed to answer a medical question. Some doctors perform ultrasounds at every checkup out of habit, simply because many of their patients expect it. If you would prefer fewer ultrasounds, let your doctor know—they may be happy to skip ultrasounds at some appointments.

On the other hand, your doctor may have a good reason to perform scans more often in your particular case. If your pregnancy is considered “high-risk,” whether due to carrying multiples, or a potential complication, the benefits of regular ultrasounds likely outweigh any possible risks, which remain theoretical and unlikely. As the FDA has noted, the weight of the evidence so far indicates that ultrasounds are very safe.[xii]

The Temptation of Home Heartbeat Monitors

Another area where common practice often conflicts with the FDA guidance is the use of fetal doppler heartbeat monitors. Many women use these devices, which can be purchased inexpensively online, to listen to their baby’s heartbeat on a daily basis, whether for fun or reassurance. Yet the FDA strongly recommends that these devices should only be used under medical supervision.

Unlike a stethoscope, which merely listens for sounds from the baby’s heartbeat, doppler heartbeat monitors actually work like ultrasounds, emitting high frequency sound waves and then converting the reflected sound waves into a heartbeat. These devices are regarded as very safe and are typically used at every doctor’s appointment but should not be used at home unless recommended by your doctor.

As noted by Dr. Shahram Vaezy, an FDA biomedical engineer, “when the product is purchased over the counter and used without consultation with a health care professional taking care of the pregnant woman, there is no oversight of how the device is used. Also, there is little or no medical benefit expected from the exposure.[xiii] Furthermore, the number of sessions or the length of a session in scanning a fetus is uncontrolled, and that increases the potential for harm to the fetus.”

The potential for any harm from the sound waves is still extremely low, but there is also the concern that using a fetal heart monitor at home without medical guidance can sometimes give false reassurance. It takes training and experience to use the devices properly, and there have been reports of women who did not seek medical attention when they noticed their baby was not moving because they used a home heart monitor and were reassured by what they believed was their baby’s heartbeat.

As The New York Times reported in an article on this problem, “it is difficult for an inexperienced person to distinguish between a baby’s heartbeat and the whooshing sounds of a mother’s own pulse or blood flow. And even when parents do find the fetal heartbeat, there is no way for them to know whether the baby is well or in distress.”[xiv]

Dr. Abhijoy Chakladar of the Princess Royal Hospital in Britain told The New York Times, “this is something that comes only with experience. In hospital, fetal health is assessed by experienced midwives and doctors who take a team approach . . .”[xv] He advises that if a mother is concerned that something has changed with her baby’s movement, she should consult her doctor instead of relying on a home fetal heart monitor. “On their own, these monitors are harmless; it is their improper use by parents to reassure themselves which can be dangerous,” he says.

Points to Remember

  • There is little evidence that prenatal ultrasounds increase the risk of autism or pose any other dangers.
  • Even so, because of the possibility that problems could be discovered in the future, the official recommendation is that ultrasounds should only be used to answer a medical question, and then only for the shortest amount of time.
  • If you would prefer to have limited ultrasounds, rather than a scan at every checkup, let your doctor know.
  • For high-risk pregnancies, the benefits of regular ultrasounds likely outweigh the potential risks.
  • Doppler heartbeat monitors are likely safe but should not be used at home unless recommended by your doctor. There are still uncertain risks from excessive use and these devices may give false reassurance, particularly to those who are untrained in how to properly use them.

[i] Rosman, N. P., Vassar, R., Doros, G., DeRosa, J., Froman, A., DiMauro, A., … & Abbott, J. (2018). Association of prenatal ultrasonography and autism spectrum disorder. JAMA Pediatrics, 172(4), 336–344.

[ii] Abramowicz, J. S. (2012). Ultrasound and autism: association, link, or coincidence?. Journal of Ultrasound in Medicine, 31(8), 1261–1269.

Grether, J. K., Li, S. X., Yoshida, C. K., & Croen, L. A. (2010). Antenatal ultrasound and risk of autism spectrum disorders. Journal of Autism and Developmental Disorders, 40(2), 238–245.

Stoch, Y. K., Williams, C. J., Granich, J., Hunt, A. M., Landau, L. I., Newnham, J. P., & Whitehouse, A. J. (2012). Are prenatal ultrasound scans associated with the autism phenotype? Follow-up of a randomised controlled trial. Journal of Autism and Developmental Disorders, 42(12), 2693–2701.

Carlsson, L. H., Saltvedt, S., Anderlid, B. M., Westerlund, J., Gillberg, C., Westgren, M., & Fernell, E. (2016). Prenatal ultrasound and childhood autism: long‐term follow‐up after a randomized controlled trial of first‐vs second‐trimester ultrasound. Ultrasound in Obstetrics & Gynecology, 48(3), 285–288.

[iii] Webb, S. J., & Mourad, P. D. (2018). Prenatal ultrasonography and the incidence of autism spectrum disorder. JAMA Pediatrics, 172(4), 319–320.

[iv] Webb, S. J., Garrison, M. M., Bernier, R., McClintic, A. M., King, B. H., & Mourad, P. D. (2017). Severity of ASD symptoms and their correlation with the presence of copy number variations and exposure to first trimester ultrasound. Autism Research, 10(3), 472–484.

[v] ACOG Committee Opinion (2017). Guidelines for Diagnostic Imaging During Pregnancy and Lactation. Number 723, October 2017.

[vi] Bricker, L., Medley, N., & Pratt, J. J. (2015). Routine ultrasound in late pregnancy (after 24 weeks’ gestation). Cochrane Database of Systematic Reviews, (6).

[vii] Bricker, L., Medley, N., & Pratt, J. J. (2015). Routine ultrasound in late pregnancy (after 24 weeks’ gestation). Cochrane Database of Systematic Reviews, (6).

[viii] Whitworth, M., Bricker, L., & Mullan, C. (2015). Ultrasound for fetal assessment in early pregnancy. Cochrane Database of Systematic Reviews, (7).

[ix] Sovio, U., White, I. R., Dacey, A., Pasupathy, D., & Smith, G. C. (2015). Screening for fetal growth restriction with universal third trimester ultrasonography in nulliparous women in the Pregnancy Outcome Prediction (POP) study: a prospective cohort study. The Lancet, 386(10008), 2089–2097.

Imdad, A., Yakoob, M. Y., Siddiqui, S., & Bhutta, Z. A. (2011). Screening and triage of intrauterine growth restriction (IUGR) in general population and high risk pregnancies: a systematic review with a focus on reduction of IUGR related stillbirths. BMC Public Health, 11(3), S1.

Breeze, A. C., & Lees, C. C. (2007, October). Prediction and perinatal outcomes of fetal growth restriction. In Seminars in Fetal and Neonatal Medicine (Vol. 12, No. 5, pp. 383–397). WB Saunders.

[x] American College of Obstetricians and Gynecologists (2017). Ultrasound Exams.

[xi] U.S. Food and Drug Administration. (2018). Ultrasound Imaging.

[xii] U.S. Food and Drug Administration. (2018). Ultrasound Imaging.

[xiii] U.S. Food and Drug Administration. (2014). Avoid Fetal “Keepsake” Images, Heartbeat Monitors.

[xiv] Parker-Pope, Tara. The Risk of Home Fetal Heart Monitor. The New York Times, November 6, 2009.

[xv] Parker-Pope, Tara. The Risk of Home Fetal Heart Monitor. The New York Times, November 6, 2009.