RESUMEN
A 28-year-old primi gravida visited our department at 20 weeks gestation. The ultrasound screening revealed twin gestation, and follow up screening revealed a bilobed large fetal neck mass in the 1st twin. We measured thyroid volume with ultrasound which was 5.072 cm3. Other fetal organs appeared normal. Cordocentesis was performed for fetal thyroid function and congenital hypothyroidism was confirmed. In addition, maternal thyroid hormones were checked. The other fetus was normal. Thyroid stimulating hormone (TSH) in the maternal serum was increased, but thyroxine (T3) was (within normal range). Two weeks later, we checked TSH and free T4 in amniotic fluid and administered intra-amniotic thyroxine (200 ?g). We repeated the procedures 2 more times in two consecutive weeks. After 3 intra-amniotic thyroxine injection, follow-up cordocentesis revealed euthyroid status of the fetus. Although the thyroid gland had decreased in size and volume, it was still goitrous. At 36 weeks of gestation, the patient was admitted for preterm premature rupture of the membranes and the twin was delivered vaginally. The 1st twin was proved as an euthyroid status and antithyroid antibody was not detected. During the 3 years follow up, the baby had no considerable developmental problem. The intrauterine recognition and treatment of congenital goitrous hypothyroidism may not only reduce the obstetric complications associated with large goiters, but possibly improve the prognosis for normal growth and mental development of affected fetuses.