An 8-year follow-up study from a randomized, controlled trial of repeated prenatal ultrasound examinations found no evidence of any lasting harm to any aspect of child development.
The initial study demonstrated that infants exposed prenatally to five ultrasound imaging studies between 18 and 38 weeks' gestation had a significantly greater risk of low birth weight than children exposed to only a single ultrasound at 18 weeks of gestation.
Included in the follow-up analysis were 1,352 children who previously had been randomized to the regular ultrasound group and 1,362 children randomized to the intensive ultrasound group (Lancet 2004;364:2038-44).
After 8 years of repeated follow-up examinations, children in the two groups showed no statistically significant differences in a wide variety of developmental measures. These included measures of physical growth, toddler temperament, language development, and behavior, reported John P. Newham, M.D., of the University of Western Australia (Subiaco), and his colleagues.
The groups showed a statistically significant difference on only a single measure of child development. At 1 year of age children in the intensive ultrasound group showed a smaller number of abnormal scores on a test of early language milestones than children in the regular ultrasound groups.
The authors suggested that this may have been a statistical fluke—a seemingly significant result that showed up by chance because of the many end points examined in the study. An alternative explanation may be that women who had repeated ultrasound examinations may have had greater awareness of the study, which in turn enhanced parental attention, resulting in earlier language acquisition.
While this study showed no deleterious effects of repeated ultrasound examinations to the developing fetus, the authors cautioned that contemporary ultrasound instruments have higher power outputs than the instruments used in the study.