Some reports of research showing ultrasound’s effects on neurological development of mice fetuses are generating interest in the popular press. Working in the lab of Pasko Rakic, Eugenius Ang and colleagues found that a “small but statistically significant number of neurons fail to acquire thier proper position” within the cerebral cortex among fetal mice exposed to 30 or more minutes of ultrasound waves during the period of time when these neurons develop.
News reports such as one by Randolph E. Schmid (Associated Press science writer) include a quotation from Dr. Rakic (Yale University) mentioning a possible connection to dyslexia and other disorders.
Rakic’s paper said that while the effects of ultrasound in human brain development are not yet known, there are disorders thought to be the result of misplacement of brain cells during their development.
“These disorders range from mental retardation and childhood epilepsy to developmental dyslexia, autism spectrum disorders and schizophrenia,” the researchers said.
The reasons for caution in extrapolating to human fetal development are many. Mr. Schmid also interviewed Joshua Copel, president-elect of the American Institute of Ultrasound Medicine and another professor at the Yale Medical School, getting additional interpretation of the findings.
Copel… did point out that there are large differences between scanning mice and scanning people.
For example, because of their size, the distance between the scanner and the fetus is larger in people than mice, which reduces the intensity of the ultrasound. In addition, he said, the density of the cranial bones in a human baby is more than that of a tiny mouse, which further reduces exposure to the scan.
The paper noted that the developmental period of these brain cells is much longer in humans than in mice, so that exposure would be a smaller percentage of their developmental period.
However, it also pointed out that brain cell development in people is more complex and there are more cells developing, which could increase the chances of some going astray.
Furthermore, previous research directly testing the hypothesis that prenatal exposure to ultrasound increases the risk of dyslexia has provided mixed-but-mostly-null results. According to the abstract of one study, Stark and colleagues found “no biologically significant differences between exposed and unexposed children,” however, some folks (e.g., here and here) say that there was a significant correlation between exposure and dyslexia; I have requested the original article so that I can review it and shall report on it once I’ve read it. Salvesen and colleagues found (1992) “that those [children] whose mothers received diagnostic ultrasound screening while pregnant did just as well on reading, spelling and arithmetic tests as those whose mothers had not” but they reported (1993) that “the odds of non-right handedness were higher among children who had been screened in utero than among control children…. No clear differences were found between the groups with regard to deficits in attention, motor control, and perception or neurological development during the first year of life” but cautioned that the findings were inconsistent.
Link to the abstract of the article by the Rakic team; there are additional links on this page from which one can see supporting material and download a PDF of the full article. Link to Mr. Schmid’s story, as carried by LiveScience. Link to an HTML page for Dr. Rakic’s lab.
Ang, E. S. B. C Jr., Gluncic, V., Duque, A., Schafer, M. E., & Rakic, P. (2006). Prenatal exposure to ultrasound waves impacts neuronal migration in mice. Proceedings of the National Academy of Science, 2006 Aug 10 [Epub ahead of print]. Retrieved 14 August 2006 from http://www.pnas.org/cgi/doi/10.1073/pnas.0605294103.
Stark, C. R., Orleans, M., Haverkamp, A. D., & Murphy, J. (1984). Short- and long-term risks after exposure to diagnostic ultrasound in utero. Obstetrics & Gynecology, 63, 194-200.
K. A. Salvesen, K. A., Bakketeig, L. S., Eik-nes, S. H., Undheim, J. O., & Okland, O. (1992). Routine ultrasonography in utero and school performance at age 8-9 years. The Lancet, 339(8785), 85(5).
Salvesen K. A., Vatten L. J., Eik-Nes S. H., Hugdahl K., & Bakketeig, L. S. (1993). Routine ultrasonography in utero and subsequent handedness and neurological development. British Medical Journal, 307(6897), 159-