A 29-year-old woman with Graves' disease is in her 6th week of pregnancy. She is currently on propylthiouracil (PTU). Her FT4 is mildly elevated. What is the recommended switch in antithyroid drug management during the second trimester?
- A Continue PTU throughout pregnancy
- B Switch to carbimazole/methimazole after the first trimester ✓
- C Switch to carbimazole/methimazole immediately
- D Stop all antithyroid drugs and use beta-blockers alone
Correct answer: B. Switch to carbimazole/methimazole after the first trimester
Explanation
PTU is preferred in the first trimester because methimazole is associated with aplasia cutis and choanal atresia (methimazole embryopathy) during organogenesis. However, PTU carries risk of severe hepatotoxicity, so current guidelines recommend switching to methimazole/carbimazole after the first trimester (from ~week 14 onwards). Continuing PTU throughout pregnancy risks liver failure. Beta-blockers alone do not treat the underlying thyrotoxicosis adequately.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.