Thyroid disease during pregnancy: options for management

Abstract

Thyroid diseases affect up to 5% of all pregnancies. Adverse pregnancy and neonatal outcomes are increased by maternal thyroid disease and adequate treatment is thought to reduce these risks. Hypothyroidism is commonly treated with levothyroxine, with pregnancy increasing levothyroxine requirements in most women treated for hypothyroidism. Hyperthyroidism is often treated with antithyroid drugs in pregnancy. However, they are not completely safe to use during pregnancy as methimazole increases risk of neonatal malformations and propylthiouracil increases risk of maternal hepatotoxicity. Propylthiouracil is recommended to be used during the first trimester and switch to methimazole is recommended thereafter to reduce risk of hepatotoxicity. The treatment goal for hypothyroidism and hyperthyroidism is to achieve euthyroidism quickly and maintain it throughout pregnancy. Autoimmune thyroiditis and isolated maternal hypothyroxinemia do not currently warrant treatment during pregnancy, unless hypothyroidism ensues. Treatment of thyroid nodules and differentiated thyroid cancer can generally be safely postponed until after delivery.

Keywords::

• antithyroid drugs
• autoimmune thyroiditis
• hypothyroidism
• hyperthyroidism
• levothyroxine
• pregnancy

Financial & competing interests disclosure

This work was supported by the Intramural Training Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • The reference intervals of thyroid function tests are different in pregnant compared with non-pregnant populations.

• • Maternal hypothyroidism affects up to 3% of all pregnancies and is associated with increased risk of adverse pregnancy and neonatal complications if untreated.

• • Levothyroxine requirements increase during pregnancy among most women with hypothyroidism. The goal of levothyroxine treatment in primary hypothyroidism is to normalize thyrotropin (TSH) levels as fast as possible.

• • Levothyroxine should be administered in the morning at least 30–60 min before breakfast. There should be at least 4–6 h between levothyroxine and iron and/or calcium supplement ingestion.

• • Maternal hyperthyroidism should preferentially be managed before conception as untreated persistent hyperthyroidism is associated with several serious pregnancy and neonatal complications.

• • Antithyroid drugs can be safely used during pregnancy to control maternal hyperthyroidism when their limitations are noted. The goal of antithyroid drug treatment is to normalize maternal free thyroxine (fT4) up to the high-normal range.

• • Isolated maternal hypothyroxinemia does not currently warrant treatment in pregnancy. Sufficiency of iodine intake should be established.

• • Autoimmune thyroiditis is associated with increased risk of hypothyroidism during pregnancy and may be associated with adverse outcomes.

• • Treatment of thyroid nodules and differentiated thyroid cancer can usually be postponed until after delivery.