Thyroid Function in Pregnancy

Abstract

The level of circulating thyroid hormone normally increases in pregnancy, and this increase can be induced in nonpregnant women and in men by administering estrogen. The reason for the rise seems to be an increase in thyroxin-binding ability of the serum proteins. The basal metabolic rate also rises in pregnancy.

The treatment of choice for thyrotoxicosis in pregnancy is the use of antithyroid drugs in amounts which are physiologic for the pregnant state but not physiologic for the nonpregnant state. Propylthiouracil is preferred. The goitrogens pass the placental barrier, but there is danger to the fetus only when the level of circulating thyroid hormone falls below the normal range for pregnancy.