A fetal goiter (enlarged thyroid) and hypothyroidism (inadequate thyroid hormone) is an uncommon but potentially serious complication of the treatment of hyperthyroidism (overactive thyroid) in pregnant women, the result of maternal Graves’ disease (autoimmune thyroid disease), or congenital hypothyroidism (low thyroid hormone at birth). Successful in utero treatment of goiter and hypothyroidism is possible with the intraamniotic administration of thyroxine (injecting thyroid medicine into the womb) via a long, thin needle under ultrasound guidance.