A 28-year-old pregnant woman at 8 weeks is newly diagnosed with Graves' disease, with suppressed TSH and raised T3 and T4. Which is the most appropriate first-line treatment?

• A. Propylthiouracil
• B. Methimazole
• C. Carbimazole
• D. Radioiodine

Answer: (A)

In early pregnancy, the priority is to control the mother’s thyroid levels while minimizing fetal risk during organ development. Propylthiouracil is favored in the first trimester because it effectively reduces thyroid hormone production and has a lower risk of causing congenital malformations when exposure occurs during early fetal development, compared with methimazole or carbimazole, which have been linked to fetal congenital abnormalities. Therefore, starting with propylthiouracil at 8 weeks gestation is the best initial approach. After the first trimester, many clinicians switch to methimazole or carbimazole to reduce the potential for hepatotoxicity associated with propylthiouracil. Radioiodine therapy is not used in pregnancy due to the risk of fetal thyroid damage from radiation.