In a pregnant woman with hyperthyroidism due to Graves' disease, which of the following is the MOST important concern regarding propylthiouracil (PTU) use in the first trimester?
- A PTU causes neural tube defects and is absolutely contraindicated throughout pregnancy
- B PTU causes neonatal hypothyroidism and should be stopped at 28 weeks
- C PTU is preferred in the first trimester because carbimazole is associated with aplasia cutis and choanal atresia ✓
- D Carbimazole has lower placental transfer than PTU and is preferred in all trimesters
Correct answer: C. PTU is preferred in the first trimester because carbimazole is associated with aplasia cutis and choanal atresia
Explanation
In pregnancy, carbimazole and methimazole are associated with rare but serious fetal anomalies — aplasia cutis congenita, choanal atresia, tracheoesophageal fistula, and 'methimazole embryopathy' — particularly with first-trimester exposure. Therefore, propylthiouracil (PTU) is preferred in the first trimester as it has not been associated with these malformations. After the first trimester, carbimazole/methimazole is preferred because PTU carries risk of rare severe maternal hepatotoxicity. This trimester-specific switching strategy is recommended by guidelines.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.