ECMUS Literature Reviews

Kieler H, Haglund B, Cnattingius S, Palmgren J, Axelsson O. Does prenatal sonography affect intellectual performance? Epidemiology 2005; 16: 304-310

This is a registry study of a possible association between exposure to ultrasound during pregnancy and intellectual performance among 18 years old males.

The information about intellectual abilities was retrieved from the Swedish National Service Register which includes the results of a battery of tests the men are submitted to when enrolling for military service at the age of 18 years. The test results are given as standard scores (maximum 9, mean 5, SD 2).

Data about the place of birth of a cohort of more than 200,000 individuals were available from the Swedish Medical Birth Register. After exclusions, two groups were compared - a group of 6026 men, supposedly exposed to ultrasound as fetuses, and a control group of 161,033 men. The exposure to ultrasound was assumed to have happened as the men of the index group were born in the Southern Swedish area served by the Malmö Department of Obstetrics and Gynecology that was the only unit in Sweden that offered an ultrasound examination as a routine for detection of multiple pregnancies and dating to all pregnant women during the years 1973-1978. Two additional comparisons were performed: the results of the index cohort were compared to the results of the period before introduction of routine ultrasound in Malmö and analyses were also performed on 15,540 pairs of brothers. The older brothers were born before, and the younger brothers after, the introduction of ultrasound examinations; in 456 of the pairs, the younger brothers were born in Malmö.

The men born in Malmö were found to have lower intellectual performance scores (mean difference -0.16; 95 % confidence interval [CI] -0.21 to -0.11) and an increased risk of subnormal performance (odds ratio [OR] 1.28; CI 1.18.1.38) as compared with the control group. However, when analysing the period before the introduction of ultrasound examinations, the men born in Malmö also had lower intellectual performance and the difference was of similar magnitude. In addition, there were no differences within brother pairs, when comparing the younger brothers, assumed to have been exposed to ultrasound, and the unexposed older brothers. Thus, the authors concluded that there was no association between ultrasound examination during pregnancy and intellectual performance in young adults.

The present study is large, and the information was collected prospectively in the registries. Nevertheless the study has limitations; possible confounding factors are largely unknown, the intellectual test used at enrolment may be questioned, and the exposure information is assumed, based only on information about the place of birth. This is adequately discussed in the paper. The results do not suggest a negative influence of ultrasound examination in pregnancy on the intellectual development in males.