Human teratogens update 2011: can we ensure safety during pregnancy?

Anniversaries of the identification of three human teratogens (i.e., rubella virus in 1941, thalidomide in 1961, and diethylstilbestrol in 1971) occurred in 2011. These experiences highlight the critical role that scientists with an interest in teratology play in the identification of teratogenic exposures as the basis for developing strategies for prevention of those exposures and the adverse outcomes associated with them. However, an equally important responsibility for teratologists is to evaluate whether medications and vaccines are safe for use during pregnancy so informed decisions about disease treatment and prevention during pregnancy can be made. Several recent studies have examined the safety of medications during pregnancy, including antiviral medications used to treat herpes simplex and zoster, proton pump inhibitors used to treat gastroesophageal reflux, and newer-generation antiepileptic medications used to treat seizures and other conditions. Despite the large numbers of pregnant women included in these studies and the relatively reassuring results, the question of whether these medications are teratogens remains. In addition, certain vaccines are recommended during pregnancy to prevent infections in mothers and infants, but clinical trials to test these vaccines typically exclude pregnant women; thus, evaluation of their safety depends on observational studies. For pregnant women to receive optimal care, we need to define the data needed to determine whether a medication or vaccine is "safe" for use during pregnancy. In the absence of adequate, well-controlled data, it will often be necessary to weigh the benefits of medications or vaccines with potential risks to the embryo or fetus.