Recent Issues Related to Thyroid Disease in Pregnancy

ABSTRACT

Maternal and fetal complications may occur because of pathologic or immunologic changes during pregnancy. The American Thyroid Association (ATA) suggests an optimal thyroid stimulating hormone (TSH) reference range of 0.50-4.00 mU/L in pregnant women. Based on Korean data, the same range may be applied to Korean pregnant women. According to the ATA guideline, levothyroxine therapy is recommended for thyroid peroxidase antibody (TPOAb)-positive women with a TSH greater than the pregnancy-specific reference range (approximately ＞4.0 mU/L in Korea) and TPOAb-negative women with a TSH ＞10.0 mU/L. The presence of TPOAb may be a sign of hypothyroidism due to damage to the thyroid. Because the titer of TPOAb decreases as gestation progresses, its measurement should be performed as early as possible during pregnancy. Although the mechanism is unknown, the association between thyroid autoimmunity and miscarriage/premature delivery is clear. Selenium may reduce the development of postpartum thyroiditis and permanent hypothyroidism; however, routine prescription of selenium is not recommended as it may increase the risk of type 2 diabetes. According to Korean nationwide data, birth defects in antithyroid drug (ATD)-exposed offspring in early pregnancy increased by 1.1 to 2.2% compared with non-exposed offspring. Avoidance of ATD in early pregnancy is the best option, otherwise, it is preferable to switch to propylthiouracil before pregnancy. When methimazole use is unavoidable in early pregnancy, it is recommended to use less than 5 mg per day.