A 29-year-old woman with a mechanical mitral valve prosthesis is planning her first pregnancy. She asks about anticoagulation risks. Which statement is correct?
- A Warfarin is safe throughout pregnancy because it does not cross the placenta
- B Warfarin between weeks 6 and 12 of gestation carries the highest risk of fetal embryopathy ✓
- C Unfractionated heparin eliminates the risk of maternal valve thrombosis entirely
- D Low molecular weight heparin crosses the placenta and causes fetal haemorrhage
Correct answer: B. Warfarin between weeks 6 and 12 of gestation carries the highest risk of fetal embryopathy
Explanation
Warfarin crosses the placenta and causes warfarin embryopathy (nasal hypoplasia, stippled epiphyses, limb anomalies) with peak risk during weeks 6 to 12 of gestation, so many guidelines favour dose adjusted low molecular weight heparin in this window. Unfractionated and low molecular weight heparins do not cross the placenta, but heparins carry higher maternal valve thrombosis rates than warfarin, so they do not eliminate maternal risk.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.