A 26-year-old woman with a metallic mitral valve prosthesis on warfarin discovers she is 6 weeks pregnant. What is the most appropriate anticoagulation strategy during the first trimester?
- A Continue warfarin throughout pregnancy at the lowest effective dose
- B Switch to aspirin 150 mg for the first trimester
- C Switch to LMWH throughout the first trimester to avoid fetal warfarin embryopathy ✓
- D Use unfractionated heparin infusion throughout the first trimester
Explanation
Warfarin embryopathy (nasal hypoplasia, stippled epiphyses, CNS abnormalities) results from warfarin use between 6–12 weeks of gestation. LMWH (therapeutic dose with anti-Xa monitoring) is preferred during the first trimester (weeks 6–12) to prevent fetal warfarin embryopathy. After 12 weeks, warfarin can be resumed until 36 weeks when delivery planning begins. Continuing warfarin is preferred mid-pregnancy as it provides superior thromboembolism protection compared to LMWH for mechanical valves, but the first-trimester switch is critical. Note: A warfarin dose ≤5 mg/day carries lower risk of embryopathy and some guidelines permit continuation if the patient is counseled and agrees, but LMWH switch remains the predominant recommendation for safety.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.