Neonatal Thyroid Function after Propylthiouracil Therapy for Maternal Graves' Disease

PROPYLTHIOURACIL (PTU) is a mainstay of medical treatment for hyperthyroidism during pregnancy.1 2 3 4 PTU inhibits thyroid-hormone synthesis, extrathyroidal conversion of thyroxine (T4) to 3,5,3′-triiodothyronine (T3), and deiodinative degradation of the hormonally inactive T4 metabolite 3,3′,5′-triiodothyronine (reverse T3 or rT3).5 6 7 8 PTU crosses the placenta, 4 and at high doses it may cause fetal goiter9 , 10 and hypothyroidism.3 Low doses of PTU, 300 mg or less daily, are thought to afford satisfactory control of maternal hyperthyroidism and are not believed to cause clinically evident thyroid dysfunction in the neonate.1 2 3 4 , 11 Neonatal goiters occur with maternal doses of 100 . . .