No clear correlation between routine ultrasonic scans and intellectual impairment

Scientists carrying out a major epidemiological study at Karolinska Institutet and Uppsala University have discovered that there is no clear correlation between routine ultrasonic scans and intellectual impairment.

"Fears have been expressed that sonography can lead to diminished intellectual capacity," explains Helle Kieler, research scientist at Karolinska Institutet.

Previous epidemiological studies have shown that young men who had been exposed to in utero ultrasonic scans are more likely than other young men to be left handed; and that there is a correlation between left-handedness and reduced intellectual capacity in children born after a complicated pregnancy.

The new study, which is to be published on 13 April in the scientific journal Epidemiology, is based on data from approximately 180,000 boys born in the 1970s, when routine ultrasonic examinations of foetal development were first introduced in Sweden. Almost 20 years later, the young men were given intelligence tests on signing up for their military service. When researchers compared the boys who had been scanned with those that had not, it transpired that intellectual capacity was lower in those who were exposed to ultrasound in during gestation. The differences, however, were small and other influences on the results could not be ruled out.

To control for such (unquantified) factors, the scientists then conducted a smaller-scale analysis of brothers. This enabled them to confirm that there was nothing to suggest that the brother who had been exposed to in utero ultrasonic radiation was intellectually inferior to the one who had not.

"The results are reassuring in terms of the risk that routine prenatal sonography has lasting effects on the development of the foetal brain," says Ms Kieler. "It is important to remember, however, that the study reflects the effects of how ultrasound was used in the 1970s. Scanning procedures have changed since then, and children born today have generally been exposed to more ultrasonic radiation than those included in the study."