Successful Intrauterine Therapy for Fetal Goitrous Hypothyroidism during Late Gestation

We experienced a case of fetal goitrous hypothyroidism in an infant delivered by a 33-year-old woman receiving 300 mg/day of propylthiouracil (PTU) for hyperthyroidism due to Graves' disease. A large fetal goiter (maximum diameter, 60 mm) was detected by magnetic resonance imaging (MRI) at 36 weeks of gestation. Initial fetal blood sampling revealed hypothyroidism with a serum thyroid-stimulating hormone (TSH) of 99 μIU/mL, free triiodothyronine (T3) of 1.97 pg/mL, and free thyroxine (T4) of 0.29 ng/dL. Consequently, a diagnosis of fetal goitrous hypothyroidism due to transplacental passage of maternal PTU was made. To reduce the risk of perinatal complications, 300 μg of levothyroxine sodium (L-T4) was administered into the maternal amniotic fluid twice between 37 and 38 weeks of gestation. Subsequent fetal MRI showed that the size of goiter had decreased. At 38 weeks and 5 days of gestation, a 3042-g male infant was born by cesarean section. There were no severe complications at delivery, although mild tachypnea was observed and the infant's thyroid gland was slightly enlarged. He was treated with L-T4 for two weeks. At present, his growth and neurological development are normal. This case indicates that intrauterine therapy by the intraamniotic administration of L-T4 can be effective in treating fetal goitrous hypothyroidism even during late gestation.