[Anticoagulant therapy during pregnancy in patients with mechanical valvular prostheses]

Anticoagulant therapy (heparin or oral anticoagulants) during pregnancy in patients with mechanical valvular prostheses should take into consideration the respective risks of the usage of these two products: thromboembolic for the mother, congenital malformations for the children and haemorrhagic for them both. Basically, heparin therapy is useful by limiting the risk of foetal complication, but it increases maternal risk, especially related to thromboembolism. The risks of oral anticoagulants are concentrated in the second half of the first trimester (coumarin-related embryopathies) and in the peri-partum period (maternal and foetal haemorrhage). There is general agreement to use oral anticoagulants outside these periods, during the second trimester and most of the third. During the first trimester, the European and North American Recommendations make provision for parental consultation. Some authors recommend oral anticoagulants even during the first trimester because of the scarcity of coumarin-related embryopathies. In fact, the incidence greatly increases when the dosage required is over 5 mg of coumarin per day. Others continue anticoagulation until the end of pregnancy, stopping 48 hours before delivery, either vaginal or by caesarean section. These attempts to avoid heparin therapy are related to difficulties of obtaining stable anticoagulation with non-fractionated heparin which increases the risk of thromboembolism, especially prosthetic valve thrombosis. Low molecular weight heparin, which is widely used in venous and arterial thromboembolic disease, including during pregnancy, is not yet recommended for usage in pregnant women with mechanical valvular prostheses because there are not results from large series concerning their efficacy and safety in this particular indication. In the absence of randomised studies in pregnancy, the renewal of small series in specialised centres will probably open up the field for their usage in the years to come.