Venous thromboembolism (VTE) results from a combination of hereditary and acquired risk factors, including surgery, venous compression or injury, smoking, obesity, race and increasing age. Pregnancy is associated with several physiologic and anatomic changes that also make pregnant and postpartum women more susceptible to VTE. Pregnancy is classified as a hypercoagulable state because fibrin generation is increased, fibrinolytic activity is decreased, and levels of coagulation factors are elevated. In addition, femoral venous pressure increases and compression of the inferior vena cava as pregnancy advances contribute to compromised venous outflow. Deep vein thromboses (DVT) account for approximately 75%-80% of VTEs in pregnant women, whereas 20%-25% of VTEs are pulmonary emboli (PE).
A leading cause of maternal mortality in the developed world, other serious consequences of VTE include post-thrombotic syndrome, chronic venous insufficiency and pulmonary hypertension. Post-thrombotic syndrome, characterized by chronic leg pain and swelling, occurs in about one-quarter of people after VTE. Chronic thromboembolic pulmonary hypertension, defined as mean pulmonary artery pressure >25 mm Hg persisting for at least 6 months after a pulmonary embolism, is less common, occurring in 2% to 4% of these patients. One-third of people who experience VTE will have long-term complications, and one-third will have a recurrence within 10 years