A 34-year-old woman with Graves' disease on methimazole for 8 months achieves euthyroidism. She is now planning pregnancy in 3 months. Which management approach is MOST appropriate?
- A Continue methimazole throughout pregnancy
- B Perform radioiodine ablation now and postpone pregnancy by 6 months
- C Switch to propylthiouracil (PTU) before conception and in first trimester, then reassess ✓
- D Stop all antithyroid drugs and monitor TSH monthly
Explanation
PTU is preferred over methimazole in the first trimester of pregnancy because methimazole is associated with a teratogenic embryopathy (aplasia cutis, choanal atresia, esophageal atresia — the MMI embryopathy). PTU crosses the placenta less and has lower teratogenic risk in the first trimester. After the first trimester (organ development complete), switching back to methimazole is recommended because PTU carries a risk of hepatotoxicity. Radioiodine is absolutely contraindicated in pregnancy and women should wait at least 6 months after RAI before conception. Stopping antithyroid drugs risks uncontrolled hyperthyroidism which is dangerous in pregnancy.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.