Warfarin is contraindicated in pregnancy, as it passes through the placental barrier and may cause bleeding in the fetus; warfarin use during pregnancy is commonly associated with spontaneous abortion, stillbirth, neonatal death, and preterm birth [REF].
When warfarin (or another 4-hydroxycoumarin derivative) is given during the first trimester-particularly between the sixth and ninth weeks of pregnancy-a constellation of birth defects known variously as fetal warfarin syndrome (FWS), warfarin embryopathy, or coumarin embryopathy can occur.