Prenatal exposure to ultrasound waves: is there a risk?

In the 6th August 2006 issue of the Proceedings of the National Academy of Sciences, Ang et al., from Pasko Rakic’s well-known laboratory at Yale University, published results of their research on neuronal migration in the mouse embryo brain and the influence of prenatal exposure to ultrasound1. In this set of experiments, the authors exposed immobilized, unanesthetized, pregnant mice to ultrasound at days 16.5–19.5 of gestation, which is the time of neuronal migration from the proliferative zone towards the brain surface. Exposure time varied from 5 to a total of 420 min (in 12 episodes each of 35 min). Their conclusion, based on the analysis of over 335 animals, was that ultrasound exposures of 30 min or more caused a derangement in the migration of neurons from the deep to the more superficial layers of the brain. In the introduction to their article, by referring to several abnormalities such as low birth weight, delayed speech and behavioral disturbances, they appear to suggest that ultrasound in general and the phenomenon of disturbed neuronal migration in particular may be to blame. This immediately set in motion some elements of the media to ‘inform’ the public of the dire dangers of ultrasound. More recently, even the political apparatus intervened: as posted on 14th November 2006, Assemblyman Joe Pennacchio, R-Montville, New Jersey, introduced legislation requesting the New Jersey Department of Health to initiate action to explore the possible relationship of sonographic examinations of pregnant patients to the increased incidence of childhood autism. According to the local paper: ‘The Assemblyman cited various scientific, published studies that show a displacement of brain cells associated with autistic children and the ability of sonograms to displace those cells.’2. It is doubtful that all of this is out of concern for the health of mouse embryos, but, naturally, because of the worry to millions of human fetuses exposed to ultrasound with or without medical indication. While the study by Ang et al.1 is important, several differences, some major, between the experimental setup and the clinical use of ultrasound in human pregnancy need to be pointed out. I present here a short discussion on whether concern is justified when performing diagnostic ultrasound.