Fetal pituitary negative feedback at early gestational age

We describe an early prenatal diagnosis and the successful treatment of fet al Graves' disease from transplacental transfer of maternal thyroid stimula ting autoantibodies (TSAb), The diagnosis of fetal thyrotoxicosis was made by umbilical cord sampling (UBS) at 20 weeks gestation, based on suppressed TSH with elevated FT4 levels. Therapy with propylthiouracil (PTU) improved fetal thyroid function tests as well as the clinical signs of fetal Graves ' disease. Three more UBS were conducted before delivery indicating persist ing mild fetal hyperthyroidism. Undetectable concentrations of thyrotrophin in fetal serum in the presence of markedly elevated FT4, suggests pituitary negative feedback at as early as 20 weeks gestation. Amniotic fluid thyrotrophin levels were measured at 20,24 and 26 weeks and were shown to correlate better with (elevated) maternal rather than (suppre ssed) fetal TSH values; therefore, we believe that amniotic fluid thyrotrop hin measurement is unreliable for prediction of fetal thyroid status, Our observation is the first documentation of an intact feedback mechanism so early in fetal development and it suggests that pituitary maturation occ urs earlier than previously believed.