Anticoagulation during pregnancy

Venous thromboembolism (VTE) occurs infrequently but is a leading cause of illness and death during pregnancy and the puerperium. In the general population the incidence of pregnancy-associated VTE is approximately 1 in 1500 deliveries. The risk of VTE is five times higher in a pregnant than in a nonpregnant woman. Postpartum the VTE risk is even higher. Women with congenital abnormalities or persistent presence of antiphospholipid antibodies have an increased risk of VTE during pregnancy and the puerperium. Women with previous VTE have an approximately 3.5-fold increased risk of recurrent VTE during pregnancy. Heparin does not cross the placenta and is therefore the anticoagulant of choice. In case of acute thrombosis during pregnancy, treatment is performed in the same manner as for nonpregnant patients. There is an ongoing debate whether pregnant women with previous venous thrombosis should routinely receive prophylactic anticoagulation. Patients who have hereditary antithrombin deficiency, antiphospholipid antibodies, a combined abnormality, or a history of a severe thrombotic event (pulmonary embolism or extended deep vein thrombosis) should be advised to use prophylactic heparin during pregnancy, starting during the first trimester. Postpartum prophylaxis should be given to all women with an increased risk for VTE. A large body of evidence has been presented that hypercoagulability may cause recurrent abortions, stillbirth, and preeclampsia. There is no doubt that the antiphospholipid syndrome is strongly associated with fetal loss. The combination of heparin and aspirin significantly decreases the fetal loss rate during pregnancy and thus this is the treatment of choice in this patient group. Several studies indicate that women with recurrent miscarriage may benefit from heparin administration during pregnancy, however, data from controlled trials have not yet been published. In women with artificial heart valves, maternal and fetal complications are frequent despite anticoagulation, but oral anticoagulants can reduce the risk for maternal complications.