Transplacental passage of anti-thyroid auto-antibodies in a pregnant womanwith auto-immune thyroid disease

We report the intra-uterine and postnatal thyroid status of a newborn, whos e mother, affected with Hashimoto's thyroiditis superimposed on a previous Graves' disease, again became hyperthyroid during the third trimester of pr egnancy. The mother had very high levels of anti-thyroid auto-antibodies, i ncluding TSH receptor auto-antibodies (TRAb) measured as TSH-binding inhibi ting auto-antibodies (TBIAb). In order to exclude fetal thyroid dysfunction due to passive transplacental transfer of TRAb, fetal blood samples were o btained by cordocentesis at 21, 27 and 32 weeks of gestation. A transplacen tal transfer of TRAb was already seen at 21 weeks, but no alteration of fet al thyroid function was present at that time. In the following weeks, a ris e in TRAb and circulating thyroid hormones was observed both in the fetus a nd mother, accompanied by overt hyperthyroidism in the mother and by growth retardation in the fetus. At birth, TRAb were shown to have stimulating ac tivity both in the newborn and mother. This report documents the early tran splacental passage of thyroid auto-antibodies and underlines the importance of close follow-up of pregnant women with auto-immune thyroid disorders. C opyright (C) 1999 John Wiley & Sons, Ltd.