Treatment of graves' disease with antithyroid drugs in the first trimester of pregnancy and the prevalence of congenital malformation.

Background: Several reports have suggested that propylthiouracil (PTU) may be safer than methimazole (MMI) for treating thyrotoxicosis during pregnancy because congenital malformations have been associated with the use of MMI during pregnancy.

Objectives: We investigated whether in utero exposure to antithyroid drugs resulted in a higher rate of major malformations than among the infants born to a control group of pregnant women.

Methods: We reviewed the cases of women with Graves' disease who became pregnant.