A prosthetic valve patient switch to heparin at which time of pregnancy:

Pregnancy following valve replacement: Mechanical valve replacement is not preferred these days as anticoagulation is required throughout pregnancy. Problem of anticoagulation: During pregnancy, the main problem is of anticoagulation. Warfarin is safe for the mother but can result in warfarin embryopathy of the fetus, miscarriage, IUGR and stillbirths. Heparin is safe for the fetus as it does not cross the placenta, but is less effective than warfarin in preventing thromboembolic events. Low molecular weight heparin is inadequate and ACOG does not recommend its use in pregnant women with prosthetic heart valves.