During pregnancy, which antithyroid drug is preferred during the first trimester?

During pregnancy, which antithyroid drug is preferred during the first trimester?

• A. Propylthiouracil preferred in the first trimester
• B. Methimazole preferred in the first trimester
• C. Radioiodine therapy
• D. Methimazole throughout pregnancy

Answer: (B)

In pregnancy, protecting fetal development during the first trimester is crucial, so the antithyroid drug chosen should minimize birth defects. Propylthiouracil is preferred in the first trimester because methimazole use early in pregnancy has been linked to teratogenic effects such as defects of the fetal skin and certain organ structures (for example, aplasia cutis and esophageal or choanal atresia). Propylthiouracil effectively reduces thyroid hormone production during this critical window, though it carries a risk of liver toxicity in the mother. After the first trimester, many guidelines recommend switching to methimazole to avoid the maternal liver toxicity associated with propylthiouracil. Radioiodine therapy is avoided during pregnancy, and using methimazole throughout pregnancy keeps the fetal teratogenic risk higher during organogenesis. So the best choice for the first trimester is propylthiouracil, with a plan to switch to methimazole later in pregnancy if needed.

In pregnancy, protecting fetal development during the first trimester is crucial, so the antithyroid drug chosen should minimize birth defects. Propylthiouracil is preferred in the first trimester because methimazole use early in pregnancy has been linked to teratogenic effects such as defects of the fetal skin and certain organ structures (for example, aplasia cutis and esophageal or choanal atresia). Propylthiouracil effectively reduces thyroid hormone production during this critical window, though it carries a risk of liver toxicity in the mother. After the first trimester, many guidelines recommend switching to methimazole to avoid the maternal liver toxicity associated with propylthiouracil. Radioiodine therapy is avoided during pregnancy, and using methimazole throughout pregnancy keeps the fetal teratogenic risk higher during organogenesis. So the best choice for the first trimester is propylthiouracil, with a plan to switch to methimazole later in pregnancy if needed.