Hyperthyroidism in pregnancy

Women with moderate to severe overt hyperthyroidism require treatment of hyperthyroidism. Thionamides are recommended. Available thionamides include propylthiouracil (PTU), methimazole (MMI), and carbimazole (CBZ), which is completely metabolized to MMI. All 3 antithyroid drugs (ATDs) have been associated with possible teratogenic effects. Compared with PTU, the effects are more common and more severe with MMI and CBZ.

Thyroid function should be monitored monthly to maintain serum free T4 concentrations in the high-normal range and serum TSH concentrations in the low-normal range. The dose of PTU should be limited to 50 mg twice daily or less becase higher doses may result in fetal goiter and hypothyroidism.