A 26-year-old pregnant woman at 10 weeks gestation is diagnosed with acute deep vein thrombosis. Anticoagulation should be managed with low molecular weight heparin rather than warfarin because:

• A Warfarin is less effective than heparin at preventing thrombus extension
• B LMWH does not cross the placenta whereas warfarin crosses and is teratogenic ✓
• C Warfarin cannot be monitored during pregnancy
• D LMWH has a longer half-life permitting once weekly dosing

Explanation

LMWH molecules are too large and polar to cross the placenta, giving no fetal anticoagulant exposure. Warfarin freely crosses the placenta and causes fetal warfarin syndrome (nasal hypoplasia, stippled epiphyses) between weeks 6 and 12, plus fetal haemorrhage and CNS abnormalities later. Warfarin can be monitored by INR in pregnancy, and LMWH is given once or twice daily by injection, not weekly.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.