Venous thromboembolic disease is a major cause of maternal morbidity and mortality. Virchow's triad of hypercoagulability, venous stasis, and vascular damage all occur during pregnancy. The risk of venous thromboembolism is five to six times higher during pregnancy and the puerperium. Risk factors include age greater than 35, antiphospholipid antibodies, inherited thrombophilias, operative delivery, increased parity, obesity, mechanical heart valves,and family history. Prophylactic and therapeutic anticoagulation is recommended for women at risk. Low molecular weight heparins are safe and effective in most cases.