Treatment of hyperthyroidism in pregnancy with propylthiouracil and methimazole

Twenty-one women were studied who had received propylthiouracil or methimazole during 26 pregnancies. Four of the infants had a goiter at birth, and 3 of these had neonatal thyrotoxicosis. In 2 children neonatal thyrotoxicosis was not evident at birth because of maternal antithyroid therapy. Five children had congenital defects. Two mothers were responsible for 4 of the children with abnormalities, and both mothers had been treated with thiourea drugs for long periods, ranging from 7 to 11 years. The majority of children who are exposed to these drugs in utero appear to have no subsequent ill effects. However, prolonged therapy with these agents may be undesirable.