Fetal goitrous hypothyroidism followed by neonatal transient hyperthyroidism. A case report.

We report a case of fetal goitrous hypothyroidism followed by neonatal transient hyperthyroidism. A fetal goiter (26 x 38 mm) was detected by ultrasound and magnetic resonance imaging at 29 weeks of gestation. Hypothyroidism was confirmed by cordocentesis, which revealed an elevated TSH (255 microIU/ml) and a low free T4 (0.4 ng/dl). The fetal goiter decreased in size after treatment with four 240-microgram intra-amniotic administrations of levothyroxine. A 2,829-gram male neonate was delivered vaginally at 37 weeks of gestation, showing an euthyroid status at birth. On day 3, free T3 was 6.9 pg/ml and free T4 was 6.4 ng/dl, indicating hyperthyroidism. This persisted for 4 months. His thyroid functions reverted to normal at 4 months of age and have been within normal range since. Undetermined factors might be involved in the development of thyroid dysfunction in the perinatal period.