Maternal-fetal transfer of thyroxine in congenital hypothyroidism due to a total organification defect or thyroid agenesis.

The fact that neonates who subsequently have severe hypothyroidism have no evidence of the condition at birth suggests the possibility of the placental transfer of thyroid hormones. It is concluded that in infants with severe congenital hypothyroidism, substantial amounts of T are transferred from mother to fetus during late gestation.