Weighing the Risks: What You Should Know about Ultrasound

By Dr Sarah J. Buckley


 Mothering  June 1, 2011 

Issue 102, September/October 2000

Pregnant belly and image of ultrasound/Ultrasonography was originally developed during World War II to detect enemy submarines. Its use in medicine was pioneered in Glasgow, Scotland, by Dr. Ian Donald, who first used ultrasound to look at abdominal tumors, and later babies in utero in the mid-1950s.1 The use of ultrasound in pregnancy spread quickly.

In westernized healthcare systems, ultrasound, which may be offered to a pregnant woman either to investigate a possible problem at any stage of pregnancy or as a routine scan at around 18 weeks, has become almost universal in pregnancy. In Australia, where I live, 99 percent of pregnant women have at least one scan, paid for in part by our federal government, through Medicare. In fact, from 1997 to 1998 Medicare paid out AU$39 million for obstetric scans, compared to AU$54 million for all other obstetric Medicare costs. In the US, the American College of Obstetrics and Gynecology (ACOG) estimates that 60 to 70 percent of pregnant women are scanned, despite an official statement from ACOG that recommends against routine ultrasound.2 At a cost of roughly $300 per procedure, this represents a cost of approximately $70 to $80 million each year in the US.

Besides routine scans, ultrasound can be prescribed to investigate problems such as bleeding in early pregnancy. Later in pregnancy, ultrasound can be used when a baby is not growing, or when breech or twin births are suspected. In such cases, the information gained from ultrasound can be very useful in decision-making, and generally most professionals support the use of ultrasound in this context.

It is such use of routine prenatal ultrasound (RPU) that is more controversial, as this practice involves scanning all pregnant women in the hope of improving the outcome for some mothers and babies. RPU seeks to gain four main types of information:

Estimated due date. Dating a pregnancy is most accurate at early stages, when babies vary the least in size. By contrast, at 18 to 20 weeks the expected date of delivery is only accurate to within a week either way. Some studies have suggested, however, that an early examination or a woman’s own estimation of her due date can be as accurate as RPU.3,4

Unsuspected physical abnormalities. While many women are reassured by a normal scan, in fact RPU detects only between 17 percent and 85 percent of the one in 50 babies that have major abnormalities at birth.5,6 A recent study from Brisbane, Australia, showed that ultrasound at a major women’s hospital missed about 40 percent of abnormalities, many of which are difficult or impossible to detect.7 The major causes of intellectual disability, such as cerebral palsy and Down syndrome, or heart and kidney abnormalities, are unlikely to be picked up on a routine scan.

There is also a small chance that the diagnosis of an abnormality is false positive. In some instances, normal babies have been aborted because of false-positive diagnoses.8 A United Kingdom survey found that one in 200 babies aborted for major abnormalities were wrongly diagnosed.9

In addition to false positives, there are also uncertain cases in which the ultrasound image cannot be easily interpreted, and the outcome for the baby is not known. In one study involving babies at higher risk of abnormalities, almost 10 percent of scans were uncertain.10 This can create immense anxiety for the woman and her family that may not be allayed by the birth of a normal baby: in the same study, mothers with questionable diagnoses still had associated anxiety three months after the child’s birth. Uncertain findings also lead to repeated and/or prolonged scans, increasing the expense, inconvenience, and dosage of ultrasound.

In some cases of uncertainty, further tests such as amniocentesis are recommended. In such situations, there may be up to two weeks wait for results, during which time a mother must consider whether or not she will terminate the pregnancy if an abnormality is found. Even mothers who receive reassuring news have felt that this process has interfered with their relationship with their babies.1

Location of the placenta. A very low-lying placenta (placenta previa) puts mother and baby at risk of severe bleeding, and usually necessitates a cesarean section. However, 19 out of 20 women who have placenta previa detected on RPU will be needlessly worried, as the placenta will effectively move upwards as the pregnancy progresses.12 Furthermore, detection of placenta previa by RPU has not been found to be safer than detection in labor.13

Multiple fetuses. Ultrasound can detect the presence of more than one baby at an early stage of pregnancy, but this knowledge affords no documented health advantages for mother or babies, and, without RPU, almost all multiple pregnancies are discovered before birth.14

Why Are RPUs So Popular?

Supporters of RPU argue that availability of ultrasonic information leads to better outcomes for mother and baby. While this seems logical, researchers have not found evidence of significant benefit from RPU, and the issue of the safety of ultrasound has not yet been resolved.

From a research perspective, the most significant benefit of RPU is a small reduction in perinatal mortality, that is the number of babies dying around the time of birth. This is, however, merely a statistical reduction since perinatal mortality rates do not include deaths that occur before five to six months’ gestation. Often when a baby is found to have a fatal abnormality on RPU, the pregnancy is terminated before this time, excluding the baby from perinatal statistics.

RPU proponents presume that early diagnosis and termination is beneficial to women and their families. However, the discovery of a major abnormality on RPU can lead to very difficult decision-making. Some women who agree to have an ultrasound are unaware that they may get information about their baby that they do not want, as they would not contemplate a termination. Other women can feel pressured to have a termination, or at least feel some emotional distancing from their “abnormal” baby.15

Furthermore, there is no evidence that women who have chosen termination are, in the long term, psychologically better off than women whose babies have died at birth. In fact, there are suggestions that the reverse may be true in some cases.16 In choosing a possible stillbirth over a termination, women at least get social acknowledgment and support, and are able to grieve openly. Where termination has been chosen, women are unlikely to share their story with others and can experience considerable guilt and pain from the knowledge that they themselves chose the loss.17

Another purported benefit of RPU is a reduced risk of being induced for being “overdue,” because RPU dating gives a more certain estimated due date. However, there is no clear evidence that this is true, as the possibility of induction is more determined by hospital or doctor policy than by the availability of RPU.19

Many supporters of RPU claim that it’s a pleasurable experience, and contributes to bonding between mother (and father, if he is present) and baby. While it is true that it can be exciting to get a first glimpse of one’s baby in utero, there is no evidence that it helps attachment or encourages healthier behavior toward the baby.20 For most women, bonding occurs naturally when they begin to feel fetal movements at 16 to 20 weeks.

Reasons for Concern

Ultrasound waves are known to affect living tissues in at least two ways. First, the sonar beam heats the highlighted area by about 1°C (2°F). This is presumed to be insignificant, based on whole-body heating in pregnancy, which seems to be safe up to 2.5°C (5°F).21 The second effect is cavitation, where the small pockets of gas that exist within mammalian tissue vibrate and then collapse. In this situation “…temperatures of many thousands of degrees Celsius in the gas create a wide range of chemical products, some of which are potentially toxic.”22 The significance of cavitation in human tissue is unknown.

A number of studies have suggested that these effects are of real concern in living tissues. The first study indicating problems analyzed cells grown in the lab. Cell abnormalities caused by exposure to ultrasound were seen to persist for several generations.23 Another study showed that, in newborn rats (who are at a similar stage of brain development as humans at four to five months in utero), ultrasound can damage the myelin that covers nerves,24 indicating that the nervous system may be particularly susceptible to damage from this technology. In 1999, an animal study by Brennan and colleagues, reported in New Scientist,25 showed that exposing mice to dosages typical of obstetric ultrasound caused a 22 percent reduction in the rate of cell division, and a doubling of the rate of cell death in the cells of the small intestine.

Studies on humans exposed to ultrasound have shown possible adverse effects, including premature ovulation,26 preterm labor or miscarriage,27, 28 low birthweight,29 poorer condition at birth,30, 31 dyslexia,32 delayed speech development,33 and less right-handedness,34, 35 a factor which in some circumstances can be a marker of damage to the developing brain. In addition, one Australian study showed that babies exposed to five or more ultrasounds were 30 percent more likely to develop intrauterine growth retardation (IUGR)–a condition that ultrasound is often used to detect.36

Two long-term randomized controlled trials, comparing exposed and unexposed children’s development at eight to nine years of age, found no measurable effect from ultrasound.37, 38 However, as the authors note, intensities used today are many times higher than in 1979 to 1981. A later report of one of these trials39 indicated that scanning time was only three minutes. More studies are obviously needed in this area, particularly in Doppler ultrasound, where exposure levels are much higher, and in vaginal ultrasound, where there is less tissue shielding the baby from the transducer.

A further problem with studying ultrasound’s effect is the huge range of output, or dose, possible from a single machine. Modern machines can give comparable ultrasound pictures using either a lower or a 5,000 times higher dose,40 and there are no standards to ensure that the lowest dose is used. Because of the complexity of machines, it is difficult to even quantify the dose given in each examination.41 In the US, as in Australia, training is voluntary (even for obstetricians), and the skill and experience of operators varies widel

In all the research done on ultrasound, there has been very little interest in women’s opinions of RPU, and the consequences of universal scanning for women’s experience of pregnancy. In her thoughtful book on prenatal diagnosis, The Tentative Pregnancy,42 Barbara Katz Rothman suggests that the large numbers of screening tests currently being offered to check for abnormalities makes every pregnancy tentative until reassuring results come back.

Ultrasound is not compulsory, and I suggest that each woman consider the risks, benefits, and implications of scanning for her own particular situation. If you decide to have a scan, be clear about the information that you do and do not want to be told. Have your scan done by an operator with a high level of skill and experience (usually this means performing at least 750 scans per year) and say that you want the shortest scan possible. If an abnormality is found, ask for counseling and a second opinion as soon as practical. And remember, it’s your baby and your choice.


1. Ann Oakley, “The History of Ultrasonography in Obstetrics,” Birth 13, no. 1 (1986): 8-13.

2. American College of Obstetricians and Gynecologists, “Routine Ultrasound in Low-Risk Pregnancy, ACOG Practice Patterns: Evidence-Based Guidelines for Clinical Issues,” Obstetrics and Gynecology 5 (August 1997) 

3. O. Olsen et al., “Routine Ultrasound Dating Has Not Been Shown to Be More Accurate Than the Calendar Method,” Br J Obstet Gynaecol 104, no. 11 (1997): 1221-1222.

4. H. Kieler, O. Axelsson, S. Nilsson, and U. Waldenstrom, “Comparison of Ultrasonic Measurement of Biparietal Diameter and Last Menstrual Period as a Predictor of Day of Delivery in Women with Regular 28-Day Cycles,” Acta-Obstet-Gynecol-Scand 75, no. 5 (1993): 347-349.

5. B. G. Ewigman, J. P. Crane, F. D. Frigoletto et al., “Effect of Prenatal Ultrasound Screening on Perinatal Outcome,” N Engl J Med 329, no. 12 (1993): 821-827.

6. C. A. Luck, “Value of Routine Ultrasound Scanning at 19 Weeks: A Four Year Study of 8849 Deliveries,” British Medical Journal 34, no. 6840 (1992): 1474-1478.

7. F. Y. Chan, “Limitations of Ultrasound,” paper presented at Perinatal Society of Australia and New Zealand 1st Annual Congress, Freemantle, 1997.

8. AIMS UK, “Ultrasound Unsound?,” AIMS UK Journal 5, no. 1 (Spring 1993).

9. I. R. Brand, P. Kaminopetros, M. Cave et al., “Specificity of Antenatal Ultrasound in the Yorkshire Region: A Prospective Study of 2261 Ultrasound Detected Anomalies,” Br J Obstet Gynaecal 101, no. 5 (1994): 392-397.

10. J. W. Sparling, J. W. Seeds, and D. C. Farran, “The Relationship of Obstetric Ultrasound to Parent and Infant Behavior,” Obstet Gynecol 72, no. 6 (1988): 902-907.

11. A. Brookes, “Women’s Experience of Routine Prenatal Ultrasound,” Healthsharing Women: The Newsletter of Healthsharing Women’s Health Resource Service (Melbourne, Australia) 5, no.s 3, 4 (December 1994-March 1995).

12. MIDIRS, Informed Choice for Professionals, Ultrasound Screening in the First Half of Pregnancy: Is It Useful for Everyone? (UK: MIDIRS and the NHS Centre for Reviews and Dissemination, 1996).

13. A. Saari-Kemppainen, O. Karjalainen, P. Ylostalo et al., “Ultrasound Screening and Perinatal Mortality: Controlled Trial of Systematic One-stage Screening in Pregnancy,” The Lancet 336, no. 8712 (1990): 387-391.

14. See Note 12.

15. See Note 11.

16. D. Watkins, “An Alternative to Termination of Pregnancy,” The Practitioner 233, no. 1472 (1989): 990, 992.

17. See Note 12.

18. Ibid.

19. Ibid.

20. Ibid.

21. “American Institute of Ultrasound Medicine Bioeffects Report 1988,” J Ultrasound Med 7 (September 1988): S1-S38.

22. Ibid.

23. D. Liebeskind, R. Bases, F. Elequin et al., “Diagnostic Ultrasound: Effects on the DNA and Growth Patterns of Animal Cells,” Radiology 131, no. 1 (1979): 177-184.

24. M. H. Ellisman, D. E. Palmer, and M. P. Andre, “Diagnostic Levels of Ultrasound May Disrupt Myelination,” Experimental Neurology 98, no. 1 (1987): 78-92.

25. Brennan et al., “Shadow of Doubt,” New Scientist 12 (June 1999): 23.

26. J. Testart, A. Thebalt, E. Souderis, and R. Frydman, “Premature Ovulation after Ovarian Ultrasonography,” Br J Obstet Gynaecol 89, no. 9 (1982): 694-700.

27. See Note 13.

28. R. P. Lorenz, C. H. Comstock, S. F. Bottoms, and S. R. Marx, “Randomised Prospective Trial Comparing Ultrasonography and Pelvic Examination for Preterm Labor Surveillance,” Am J Obstet Gynecol 162, no. 6 (1990): 1603-1610.

29. J. Newnham, S. F. Evans, C. A. Michael et al., “Effects of Frequent Ultrasound During Pregnancy: A Randomised Controlled Trial,” The Lancet 342, no. 8876 (1993): 887-891.

30. S. B. Thacker, “The Case of Imaging Ultrasound in Obstetrics: A Review,” Br J Obstet Gynaecol 92, no. 5 (1985): 437-444.

31. J. P. Newnham et al., “Doppler Flow Velocity Wave Form Analysis in High Risk Pregnancies: A Randomised Controlled Trial,” Br J Obstet Gynaecol 98, no. 10 (1991): 956-963.

32. C. R. Stark, M. Orleans, A. D. Havercamp et al., “Short and Long Term Risks after Exposure to Diagnostic Ultrasound in Utero,” Obstet Gynecol 63 (1984): 194-200.

33. J. D. Campbell et al., “Case-control Study of Prenatal Ultrasonography in Children with Delayed Speech,” Can Med Ass J 149, no. 10 (1993): 1435- 1440.

34. K. A. Salvesen, L. J. Vatten, S. H. Eik-nes et al., “Routine Ultrasonography in Utero and Subsequent Handedness and Neurological Development,” British Medical Journal 307, no. 6897 (1993) 159-164.

35. H. Kieler, O. Axelsson, B. Haguland et al., “Routine Ultrasound Screening in Pregnancy and the Children’s Subsequent Handedness,” Early Human Development 50, no. 2 (1998): 233-245.

36. See Note 31.

37. K. A. Salvesen, L. S. Bakketeig, S. H. Eik-nes et al., “Routine Ultrasonography in Utero and School Performance at Age 8-9 Years,” The Lancet 339, no. 8785 (1992):85-89.

38. H. Kieler, G. Ahlsten, B. Haguland et al., “Routine Ultrasound Screening in Pregnancy and the Children’s Subsequent Neurological Development,” Obstet Gynecol 91, no. 5 (1998): 750-756.

39. See Note 37.

40. H. B. Meire, “The Safety of Diagnostic Ultrasound,” Br J Obstet Gynaecol 94 (1987): 1121-1122.

41. K. J. W. Taylor, “A Prudent Approach to Ultrasound Imaging of the Fetus and Newborn,” Birth 17, no. 4 (1990): 218-223.

42. Barbara Katz Rothman, The Tentative Pregnancy: How Amniocentesis Changes the Experience of Motherhood (New York: W. W. Norton, 1993).


For more information on ultrasound, see the following articles in past issues of Mothering: “Ultrasound: More Harm Than Good?” no. 77; “The Trouble with Ultrasound,” no. 57; “How Sound Is Ultrasound?” no. 34; “Ultrasound,” no. 24; and “Diagnostic Ultrasound,” no. 19.

Sarah Buckley (40) is a New Zealand-trained GP (family MD), and still in training as partner to Nicholas. Mother of Emma (9), Zoe (6), and Jacob (4), she is currently expecting her fourth baby and lives in Brisbane, Australia, where she writes about pregnancy, birth, and parenting.