Hyperthyroidism during pregnancy treated with propylthiouracil. The significance of maternal and foetal parameters.

Hyperthyroidism during pregnancy may be dangerous to the infant. The major risks are prematurity and neonatal thyrotoxicosis. The latter may be due to placental transfer of thyroid stimulating immunoglobulins from mother to fetus. Of two siblings of a previously thyrotoxic mother the first had marked symptoms of neonatal thyrotoxicosis after a pregnancy where no antithyroid treatment was given. The second child had only minimal thyrotoxic symptoms but almost as high levels of thyroid hormones as the first. During the second pregnancy propylthiouracil was given to the mother from 26 weeks' gestation, because of increased fetal movements and fetal tachycardia. Fetal movements and fetal heart rate were considered to be most valuable indicators of thyroid function in the fetus. Intense control is necessary from the beginning of the second trimester.