Thyroid disease during pregnancy.

Physiologic changes in metabolism may make thyroid diseases difficult to diagnose during pregnancy. Such diagnoses depend principally on clinical acumen and an understanding of the alterations of laboratory values, particularly thyroid-stimulating hormone (TSH), induced by pregnancy. Untreated thyrotoxicosis may lead to abortion, stillbirth, neonatal death and low birth weight. The principal cause of thyrotoxicosis in pregnancy is Graves' disease, which may be treated with antithyroid drugs or surgery. The use of radioactive iodine is absolutely contraindicated during pregnancy. Hypothyroidism during pregnancy is associated with hypertension and premature labor. The goal of thyroxine replacement therapy is to maintain serum TSH levels in the normal range. Many thyroid conditions and treatments directly affect the fetus and the principal antithyroid drugs are secreted in breast milk. Both the mother and neonate require monitoring. In addition, autoimmune postpartum thyroiditis may recur following each pregnancy in susceptible patients.