Patients with mechanical valve
prostheses are at high risk for thromboembolic events, valve
thrombosis and mortality during pregnancy. The most effective anticoagulation for the mother is achieved with oral
anticoagulants which may be associated with
embryopathy in the baby. The risk of
embryopathy and the risk of
hemorrhage during the remainder of the pregnancy depend on the intensity of anticoagulation induced in the fetus and the dose of the oral
anticoagulant used. Recent studies suggest that a
warfarin dose of less than 5 mg and an INR of less than 3 does not induce
embryopathy and is associated with a low rate of fetal complications (15%).
Heparin has been recommended as the
anticoagulant of choice during pregnancy, because it does not cross the placental barrier and does not cause
embryopathy. Yet all forms of
unfractionated heparin application (low dose, aPTT-ratio-adjusted, during the entire pregnancy or during the first trimester) are associated with a higher rate of maternal complications and death than oral
anticoagulants given throughout pregnancy until the 36th week of pregnancy. Also the total fetal outcome (abortion and
stillbirth) is not improved by
heparin. To avoid fetal and maternal complications, particularly
hemorrhage during
premature labor, mothers should be admitted to the hospital in the 36th week for conversion from oral
anticoagulants to
heparin, preferentially given i.v. prior to delivery. Vaginal delivery should be avoided under therapeutic oral anticoagulation and
cesarean section preferred after neutralization of anticoagulation. The optimal INR-monitored intensity of anticoagulation by the patient is one promising way to reduce complications and increase efficacy and safety. Randomized studies including
low molecular weight heparin and oral
anticoagulants in patients with mechanical valve
prostheses are needed, with careful monitoring of laboratory parameters and cardiac follow-up. This requires close cooperation between cardiologists, gynecologists and hemostaseologists.