Thyroid Disease (See also Chap. 335) In pregnancy, the estrogen-induced increase in thyroxine-binding globulin causes an increase in circulating levels of total T 3 and total T4. The normal range of circulating levels of free T4, free T3, and thyroidstimulating hormone (TSH) remain unaltered by pregnancy. The thyroid gland normally enlarges during pregnancy. Maternal hyperthyroidism occurs at a rate of ~2 per 1000 pregnancies and is generally well tolerated by pregnant women. Clinical signs and symptoms should alert the physician to the occurrence of this disease. Many of the physiologic adaptations to pregnancy may mimic subtle signs of hyperthyroidism. Although. | Chapter 007. Medical Disorders during Pregnancy Part 6 Thyroid Disease See also Chap. 335 In pregnancy the estrogen-induced increase in thyroxine-binding globulin causes an increase in circulating levels of total T3 and total T4. The normal range of circulating levels of free T4 free T3 and thyroidstimulating hormone TSH remain unaltered by pregnancy. The thyroid gland normally enlarges during pregnancy. Maternal hyperthyroidism occurs at a rate of 2 per 1000 pregnancies and is generally well tolerated by pregnant women. Clinical signs and symptoms should alert the physician to the occurrence of this disease. Many of the physiologic adaptations to pregnancy may mimic subtle signs of hyperthyroidism. Although pregnant women are able to tolerate mild hyperthyroidism without adverse sequelae more severe hyperthyroidism can cause spontaneous abortion or premature labor and thyroid storm is associated with a significant risk of maternal mortality. Hyperthyroidism in Pregnancy Treatment Hyperthyroidism in pregnancy should be aggressively evaluated and treated. The treatment of choice is propylthiouracil. Because it crosses the placenta the minimum effective dose should be used to maintain free T4 in the upper normal range. Methimazole crosses the placenta to a greater degree than propylthiouracil and has been associated with fetal aplasia cutis. Radioiodine should not be used during pregnancy either for scanning or treatment because of effects on the fetal thyroid. In emergent circumstances additional treatment with beta blockers and a saturated solution of potassium iodide may be necessary. Hyperthyroidism is most difficult to control in the first trimester of pregnancy and easiest to control in the third trimester. The goal of therapy for hypothyroidism is to maintain the serum TSH in the normal range and thyroxine is the drug of choice. Children born to women with an elevated serum TSH and a normal total thyroxine during pregnancy have impaired performance on .
