A pregnant woman at 10 weeks has a mechanical prosthetic mitral valve. Which anticoagulation regimen carries the highest risk to the fetus but is most effective for maternal thromboprophylaxis?
- A Low molecular weight heparin throughout pregnancy
- B Warfarin throughout pregnancy, with heparin near term ✓
- C Aspirin alone throughout pregnancy
- D Unfractionated heparin throughout pregnancy
Correct answer: B. Warfarin throughout pregnancy, with heparin near term
Explanation
Warfarin is the most effective anticoagulant for preventing thromboembolic complications in mechanical prosthetic valves, but it is teratogenic (warfarin embryopathy — nasal hypoplasia, stippled epiphyses, CNS defects) when used in the first trimester, especially at doses >5 mg/day. Despite fetal risk, warfarin throughout pregnancy (with heparin substitution from 36 weeks for delivery) offers superior maternal protection. LMWH is safer for the fetus but is less reliable for preventing valve thrombosis in mechanical valves.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.