What is the recommended antithyroid drug strategy in pregnancy?

• A. PTU in all trimesters.
• B. PTU in the first trimester; methimazole in the second and third.
• C. Methimazole in the first trimester; PTU later.
• D. Radioactive iodine therapy is preferred.

Answer: (B)

The key idea is balancing fetal safety with maternal health by choosing an antithyroid drug that minimizes risks at different stages of pregnancy. Methimazole in early pregnancy has been linked to congenital malformations, so it is avoided during the first trimester. Propylthiouracil (PTU) has a lower risk of these birth defects in early pregnancy, so it is preferred in the first 12 weeks. After organogenesis, the risk of PTU’s serious liver toxicity becomes more of a concern with longer use, so switching to methimazole in the second and third trimesters reduces this maternal risk while still controlling maternal hyperthyroidism. Radioactive iodine therapy is not used in pregnancy because it can destroy the fetal thyroid. So, the recommended strategy is PTU in the first trimester, then methimazole for the second and third trimesters.