Pregnancy-associated thrombosis.

The main reason for the increased risk of thromboembolism in pregnancy is hypercoagulability, which has likely evolved to protect women from the bleeding challenges of miscarriage and childbirth. Women are at a 4- to 5-fold increased risk of thromboembolism during pregnancy and the postpartum period compared with when they are not pregnant. Eighty percent of the thromboembolic events in pregnancy are venous, with an incidence of 0.49 to 1.72 per 1000 pregnancies. Risk factors include a history of thrombosis, inherited and acquired thrombophilia, maternal age greater than 35, certain medical conditions, and various complications of pregnancy and childbirth. Despite the increased risk of venous thromboembolism (VTE) during pregnancy and the postpartum period, most women do not require anticoagulation. Candidates include women with current VTE, a history of VTE, thrombophilia and a history of poor pregnancy outcome, or risk factors for postpartum VTE. The intensity of the anticoagulation will depend on the indication and the monitoring will depend on the intensity. At the time of delivery, anticoagulation should be manipulated to reduce the risk of bleeding complications while minimizing the risk of thrombosis. There are no large trials of anticoagulants in pregnancy, and recommendations are based on case series, extrapolations from nonpregnant patients and the opinion of experts. Nonetheless, anticoagulants are believed to improve the outcome of pregnancy for women who have, or have had, VTE.