Thyroid Hormone Analogs and Fetal Goiter*

Abstract

Transfer of idothyronine across the placenta in most species occurs only with difficulty. Biologically active, nonhalogenated thyroid hormone analogs were recently synthesized with properties which might favor placental transfer. The doses of T3 [triiodothyronine], T4 [thyroxine] and thyroid hormone analogs necessary to prevent propylthiouracil-induced goiter formation in rat fetuses were compared. T4 and T3 prevented fetal goiter, but in doses that caused maternal hyperthyroidism; the thyroid hormone analogs prevented fetal goiter in doses that were not thyrotoxic to the mother.