Teratogenic effects of anticonvulsants.

The incidence of malformations in fetal mice exposed to phenytoin depends on drug dosage and the strain of mice. Animal research also suggests that most anticonvulsants are teratogenic in experimental animals when large doses are used, but the effect of valproate sodium on the fetus is poorly known. Cleft lip and palatal defects have been most extensively studied, but defects have also been noted in eyes, heart, and limb buds. Data from humans are less clearer than the animal data, but human maternal exposure to anticonvulsants may increase infant clefting by threefold to tenfold. If a woman at risk for childbearing is given anticonvulsants for the first time, carbamazepine may be given first. Before pregnancy, the true need for anticonvulsants should be reassessed, but abrupt discontinuation of anticonvulsants during pregnancy is not now recommended.