Normal pregnancy is accompanied by an increase in clotting factors. The resulting hypercoagulable state has likely evolved to protect women from hemorrhage at the time of miscarriage and childbirth. During pregnancy, women are 4 times more likely to suffer from venous thromboembolism (VTE) compared with when they are not pregnant. Relative to pregnancy, the risk postpartum is even higher. The incidence of VTE is approximately 2 per 1,000 births, and VTE accounts for 1 death per 100,000 births, or approximately 10% of all maternal deaths. The most important risk factors during pregnancy are thrombophilia and a history of thrombosis. A history of thrombosis increases the risk for VTE to 2% to 12%. Thrombophilia increases not only the risk for maternal thrombosis but also the risk of poor pregnancy outcome. Despite the increased risk for thrombosis during pregnancy and the postpartum period, most women do not require anticoagulation. Those who do require anticoagulation include women with current VTE, women on lifelong anticoagulation, and many women with thrombophilia or a history of thrombosis. Recommended options for anticoagulation in pregnancy are limited to heparins, which do not cross the placenta. Low-molecular-weight heparin (LMWH) is preferred over unfractionated heparin because LMWH has a longer half-life and is presumed to have fewer side effects. The longer half-life is a disadvantage around the time of delivery, when unfractionated heparin, with its shorter half-life, is easier to manage. For women who develop or are at high risk for heparin-induced thrombocytopenia or severe cutaneous reactions, fondaparinux is probably the agent of choice. Women who do not require lifelong anticoagulation, but require anticoagulation during pregnancy, will still require anticoagulation for the first 6 weeks postpartum.