PRENATALLY-DIAGNOSED NEONATAL GOITER REVE ALING TRANSIENT HYPOTHYROIDISM IN THE MOTHER

Fetal goiter is a rare occurrence that can reveal fetal thyroid dysfun ction requiring prenatal hormone replacement therapy. A case of fetal goiter diagnosed on an ultrasonogram done at 21 weeks of gestational a ge is reported, Laboratory tests found evidence of maternal hypothyroi dism (TSH, 20 mu U/ml [N < 5]; free T3, 1.3 pg/ml [N > 2.2]; and free T4, 4.6 pg/ml [N > 6]). L-thyroxine was given. Investigations for a ca use were unrewarding, Amniotic fluid studies demonstrated fetal hypoth yroidism. Follow-up tests showed worsening of the maternal hypothyroid ism and expansion of the fetal goiter, The dose of L-thyroxine given t o the mother was increased, and 300 mu g of L-thyroxine were injected into the amniotic cavity. The goiter was still present at birth at 34 weeks gestational age, and tests done on cord blood supported the diag nosis of prenatal hypothyroidism (TSH, 500 mu U; free T3, 0.5 pg/ml [N > 0/7]; and free T4, 26 pg/ml [> 60]). In the neonate, thyroid functi on tests returned to normal within four days and the size of the thyro id within six weeks. The mother required replacement therapy (100 mu g L-thyroxine per day) for eight months. Low titers of autoantibodies w ere detected in the mother. Some fetal goiters due to autoimmunity hav e no impact on thyroid function and consequently do not require replac ement therapy. However, in the case reported here the injection of L-t hyroxine into the amniotic cavity may have brought the fetal thyroid f unction to normal.