Fetal goitrous hypothyroidism. A new diagnostic and therapeutic approach.

We present a first case in whom fetal hypothyroidism with goiter was both successfully diagnosed and treated in utero. An obstetrical sonogram at 33 weeks revealed a bilobed fetal neck mass, compatible with enlarged thyroid gland, associated with neck hyperextension, reduced gastric fluid, and polyhydramnios. Umbilical blood sampling after volume reduction amniocentesis confirmed fetal hypothyroidism with a euthyroid mother. Fetal T4 measured 1.3 micrograms/dl, free T4 0.3 ng/dl, and thyroid-stimulating hormone 186 microU. Intraamniotic levothyroxine, 500 micrograms, was given twice with a 14-day interval. The head flexed, gastric fluid increased, and amniotic fluid levels returned to normal. Prenatal (36 weeks) and neonatal blood sampling demonstrated return to euthyroid indices. Ultrasonic estimates of thyroid volume decreased by over 50%. Vaginal delivery at 39 weeks was uncomplicated. The newborn appeared normal and is being maintained on thyroid replacement therapy.