The possible relation between postpartum exacerbation of hyperthyroidism and neonatal thyrotoxicosis.

Hyperthyroidism is generally considered to be ameliorated during pregnancy, and there appears to be a high incidence of postpartum exacerbation. These phenomena have to our knowledge not been related to neonatal thyrotoxicosis, a transient hyperthyroidism seen only in newborns of previous or current hyperthyroid mothers. The first of two siblings of a previously thyrotoxic mother had marked symptoms of neonatal thyrotoxicosis and high levels of thyroid hormones. The mother had not received antithyroid treatment during her first pregnancy. During her next pregnancy she was treated with propylthiouracil from the second trimester. This infant had only minimal thyrotoxic signs but almost as high levels of thyroid hormones during the neonatal period as the elder. The mother had no signs of postpartum exacerbation but her thyroid hormones were significantly elevated in the postpartum period analogous to the infants. Neither the mother nor the infants presented any increase in thyroid-stimulation hormone and long-acting thyroid stimulator during the hyperthyroid periods. The possibility is discussed, that postpartum exacerbation of hyperthyroidism and neonatal thyrotoxicosis may be related. They could be the result of a changed balance between a thyroid stimulator and an inhibitor after birth.