Approaches to the treatment of Graves’ disease during the course of pregnancy may vary, depending on the point during pregnancy at which a diagnosis is confirmed and the severity of any associated thyrotoxicosis.
Mild cases of Graves’ disease identified during later stages of pregnancy may only be monitored with serial thyroid function tests to check for evidence of progression. For reasons that are somewhat unclear, the level of hyperthyroidism associated with Graves’ disease tends to decline during the third trimester of pregnancy. In some cases, levels of hyperthyroidism may decline to the point where there may not be any evidence of thyrotoxicosis by the time of delivery.
Moderate cases of Graves’ disease identified during earlier stages of pregnancy are usually treated with antithyroid drugs. Propylthiouracil is usually the medication of choice in this situation, as there is some concern that treatment with methimazole may increase the risk of an infant developing a condition called aplasia cutis characterized by a defect in coverage of the scalp. The principal goals of treatment with antithyroid drugs may be modified during pregnancy, as there is some concern that overaggressive treatment may suppress production of thyroid hormone to levels that may interfere with the growth and development of the fetus. Thyroid function tests are usually checked at regular intervals throughout the course of pregnancy so doses of antithyroid drugs can be adjusted to maintain thyroid hormone levels in ranges that are just below the upper limits of reference ranges. In some cases it may be possible to hold or discontinue treatment if there is evidence of remission during the third trimester of pregnancy. Beta blockers may be used on a temporary basis to control symptoms related to exposure to excess amounts of thyroid hormone during pregnancy. Continued use of beta blockers throughout the course of pregnancy may be discouraged, as there is some concern that prolonged treatment may interfere with the growth and development of a fetus. Radioactive iodine cannot be used to treat Graves’ disease during pregnancy, as exposure to radioactive iodine could cause irreversible damage to the fetal thyroid gland.
In cases where thyrotoxicosis associated with Graves’ disease during pregnancy may be severe enough to pose a threat to the health of a mother or fetus, thyroid surgery may be considered as an option for treatment. This approach offers the advantage of providing immediate control of the production and secretion of excess amounts of thyroid hormone. If it is at all possible, thyroid surgery during pregnancy should be performed during the second trimester of gestation. Exposure to general anesthesia during the first trimester may be associated with an increased risk of congenital birth defects, while exposure during the third trimester may be associated with an increased risk of premature labor. Thyroid surgery may also be considered as an option for the treatment of pregnant women with moderate to severe Graves’ disease who cannot tolerate antithyroid drugs.