A 34-year-old woman presents with palpitations, heat intolerance, weight loss, and bilateral proptosis. TSH is <0.01 mIU/L, free T4 is 4.8 ng/dL. Anti-TSH receptor antibody (TRAb) is strongly positive. She is 10 weeks pregnant. The safest definitive treatment for her Graves hyperthyroidism at this gestational age is:

• A Radioiodine (I-131) ablation
• B Propylthiouracil (PTU) during first trimester ✓
• C Methimazole throughout pregnancy
• D Total thyroidectomy in first trimester

Explanation

In pregnancy, PTU is preferred over methimazole in the first trimester because methimazole is associated with aplasia cutis and choanal/esophageal atresia (embryopathy) in the first trimester. PTU is considered safer during organogenesis (weeks 6–10). After the first trimester, switching to methimazole is typically recommended because PTU carries a risk of rare but severe maternal hepatotoxicity (fulminant hepatic failure). Radioiodine is absolutely contraindicated in pregnancy (concentrates in fetal thyroid after 10–12 weeks and causes fetal hypothyroidism). Surgery is reserved for cases refractory to antithyroid drugs, preferably in the second trimester.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.