Thyroid function and 3,3'-diiodothyronine sulfate cross-reactive substance (compound W) in maternal hyperthyroidism with antithyroid treatment.

Objective: To test whether the serial measurement of maternal levels of compound W, a 3,3'-diiodothyronine sulfate cross-reactive substance, can serve as a potential indicator of fetal thyroid function in pregnant women receiving antithyroid medication.

Methods: Compound W was measured repeatedly in serum of pregnant women with hyperthyroidism treated with antithyroid medication. Free thyroxine levels of mothers and serum thyroid-stimulating hormone levels of 1-day-old neonates were analyzed by local clinical or state laboratories.

Pretreatment with propylthiouracil but not methimazole reduces the therapeutic efficacy of iodine-131 in hyperthyroidism.

Ninety-three hyperthyroid patients were treated with 1 dose of iodine-131 (131I) during the past 10 years. Thirty-three were pretreated with propylthiouracil (PTU), 22 with methimazole (MMI), and 38 received no antithyroid drugs (ATD). ATD were discontinued 5-55 days before 131I therapy in three fourths of the cases and more than 4 months before therapy in one fourth of the cases.