Assessing the safety of drugs in pregnancy: the role of prospective cohort studies.

Since, for obvious reasons, systematic testing of the teratogenic properties of drugs in humans is not possible in the premarketing phase, the epidemiological approaches to postmarketing risk evaluation are of major importance. Cohort studies, with their prospective exposure assessment, their ability to study even exposure to drugs not commonly used in pregnancy, and their ability to monitor both adverse and beneficial fetal outcomes, seem to be the most promising study type from a methodological viewpoint. Although there are numerous cohort studies on the harmful effects of drug use in pregnant women, only a few have been able to demonstrate a risk in terms of an increase in the prevalence of malformations. Most studies with significant findings were those investigating the risk potential of one group of drugs, the anticonvulsants. The lack of cohort studies showing a risk for drug use in pregnancy, however, is not necessarily indicative of some methodological deficiency. Rather, it may suggest that, for the majority of drugs, their use in pregnancy is not associated with an increased risk of congenital malformations.