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Ultrasound in pregnancy.

Routine ultrasound screening during pregnancy has become the norm in Western countries, but its benefits and risks have not yet been conclusively determined. A 2010 Cochrane systematic review found evidence that using Doppler ultrasound to monitor the fetus during high-risk pregnancies "may reduce caesarean sections and the number of babies who die." The review used data from 18 studies of varying quality with a total of 10,000 women with high-risk pregnancies (e.g., women with hypertension or diabetes, those carrying growth-restricted babies, or those who had previously miscarried). The review's authors suggest that the use of ultrasound may have helped practitioners choose treatments that improved outcome. The conclusions of this review are not definitive. Lead researcher Zarko Alfirevic (University of Liverpool, UK) would like "a higher quality, multi-centre trial of Doppler ultrasound than we have so far seen." Although ultrasound screens may have benefits in high-risk pregnancies, I was unable to find definitive evidence that ultrasound screening, which has been used for over 30 years, makes any difference in the outcome of normal pregnancies.

The question of ultrasound's benefit is important because the screening may have risks to the developing fetus. Preliminary research showed that stress proteins, not caused by heat (which is a possible effect of ultrasound energy), arose in chick embryos exposed to ultrasound, according to a statement by FDA Center for Devices and Radiological Health. In a 2006 study, neurons failed to migrate to their appropriate position in the cerebral cortex in mice exposed to high doses of ultrasound while in utero. Applying the results of this study to human babies has been criticized because mice skulls are not as thick as humans'. Also, the mice in this study, conducted by Pasko Rakic, MD, and colleagues, were exposed to far longer and higher doses than a human fetus would receive. We don't know at what point, if at all, a dose can affect an infant's brain and central nervous system. Studies have shown a correlation between increased ultrasound exposure and delayed speech in children. The incidence of restricted fetal growth also increases as ultrasound exposure increases. (A 2004 Lancet study shows that growth and development among children who had multiple prenatal ultrasound scans are comparable with that of children who received only one scan by 1 year and up to 8 years of age.) The evidence is strong enough that the FDA and medical associations have taken a stand against "keepsake" ultrasound photos and videos.

Does an ultrasound lack risk simply because a healthcare practitioner is the person performing it? During the 1930s, X-rays were used "to diagnose pregnancy and to measure the growth and normality of the fetus," writes Marsden Wagner. A 1937 standard textbook reassured readers that X-ray examination posed no danger to the fetus" ... if the examination is carried out by a competent radiologist or radiographer." Years later, research showed that these routine examinations were causing childhood cancer.

Accuracy of prenatal ultrasound screenings is another factor. Accuracy depends upon the quality of the equipment and the skill of the person using it. Even then, results are not always correct. As with any test, false-positive results (during which a baby is wrongly diagnosed as having a problem) and false-negative results (the baby has a problem not found with ultrasound) are possible. As Zarko Alfirevic says, it is not the screening itself that determines outcome. The deciding factor is how practitioners intervene. It's exciting to see pictures of the growing baby in the womb, but is it necessary--especially during normal pregnancies?

Alfirevic A, Stampalija T, Cyte GML. Fetal and umbilical Doppler ultrasound in high-risk pregnancies. Cochrane Database of Systematic Reviews. 2010;1. Art, CD007529. DOI: 10.1002/14651858. CD007529.pub2.

FDA Center for Devices and Radiological Health. Ultrasound bioeffects: effects on embryonic development and cardiac function. Available at: www.obgyn.net/ultrasound/ultrasound.asp?page=/fm/news_articles/fda_ultrasoundequip0304#embryo. Accessed January 28, 2010.

Newnham JP, Doherty DA, Kendall GE, Zubrick SR, Landau LL, Stanley FJ. Effects of repeated prenatal ultrasound examinations on childhood outcome up to B years of age: follow-up of a randomized controlled trial. Lancet. December 4, 2004:364(9450):2038-2044.

Smith M. Ultrasound affects development of murine brains. Medpage Today. August 8, 2006. Available at: www.medpagetoday.com. Accessed January 28, 2010.

Wagner M. Ultrasound: more harm than good? Midwifery Today. Summer 1999. Available at: www.midwiferytody.com/articles/ultrasoundwagner.asp. Accessed January 27, 2010.

briefed by Jule Klotter

jule@townsendletter.com
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Title Annotation:Shorts
Author:Klotter, Jule
Publication:Townsend Letter
Geographic Code:4EUUK
Date:Apr 1, 2010
Words:742
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