A 29-year-old woman with Graves' disease achieves euthyroidism on carbimazole. She becomes pregnant at 8 weeks of gestation. What is the preferred management change?

• A Continue carbimazole throughout pregnancy
• B Perform radioiodine ablation immediately
• C Stop antithyroid drug and monitor only TSH
• D Switch to propylthiouracil for the first trimester ✓

Explanation

Carbimazole (and methimazole) is associated with aplasia cutis and choanal/oesophageal atresia when used in the first trimester (embryopathy). Propylthiouracil (PTU) is the drug of choice in the first trimester because this embryopathy risk does not occur with PTU. After the first trimester, the switch back to carbimazole is preferred because PTU carries a risk of hepatotoxicity. Radioiodine is absolutely contraindicated in pregnancy.

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

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Written and medically reviewed by the StethoPrep medical team.