The risk of venous thrombosis and pulmonary embolism in otherwise healthy women is considered highest during pregnancy and the puerperium. Indeed, in a recent study from the United Kingdom of nearly 1 million reproductive-aged women, the risks of venous thromboembolism for those during the third trimester and the first 6 weeks postpartum were calculated to be six and 22 times higher, respectively, than for nonpregnant women (Sultan, 2011). The incidence of all thromboembolic events averages approximately 1 per 1000 pregnancies, and about an equal number are identified antepartum and in the puerperium. In a study from Norway of more than 600,000 pregnancies, Jacobsen and colleagues (2008) reported that deep-vein thrombosis alone was more frequent antepartum, whereas pulmonary embolism was more common in the first 6 weeks postpartum.
Venous thromboembolism frequency during the puerperium has decreased remarkably as early ambulation has become more widely practiced. Even so, the thromboembolism rate has increased significantly during the past two decades (Callaghan, 2012). Although this increase may reflect the higher sensitivities of newer diagnostic modalities, pulmonary embolism still remains a leading cause of maternal death in the United States (Table 1-3, Severe Maternal Morbidity) (O’Connor, 2011). Specifically, Berg and associates (2010) reported that approximately 10 percent of pregnancy-related maternal deaths in the United States between 1998 and 2005 were caused by thrombotic pulmonary embolism.
Rudolf Virchow (1856) postulated that stasis, local trauma to the vessel wall, and hypercoagulability predisposed to venous thrombosis development. The risk for each of these increases during normal pregnancy. For example, compression of the pelvic veins and inferior vena cava by the enlarging uterus renders the lower extremity venous system particularly vulnerable to stasis. From their review, Marik and Plante (2008) cite a 50-percent reduction in venous flow velocity in the legs that lasts from the early third trimester until 6 weeks postpartum. This stasis is the most constant predisposing risk factor for venous thrombosis. Venous stasis and delivery may also contribute to endothelial cell injury. Last, as listed in the Appendix (Serum and Blood Constituents), marked increases in the synthesis of most clotting factors during pregnancy favor coagulation.
Risk factors for developing thromboembolism during pregnancy are shown in Table 52-1. The most important of these is a personal history of thrombosis. Indeed, 15 to 25 percent of all venous thromboembolism cases during pregnancy are recurrent events (American College of Obstetricians and Gynecologists, 2011). The magnitude of other risk factors was estimated by James and coworkers (2006) using data from the Agency for Healthcare Research and Quality of all hospital discharges during 2000 and 2001. They identified the diagnosis of venous thromboembolism in 7177 women during pregnancy and 7158 during the postpartum period. Calculated risks for thromboembolism were approximately doubled in women with multifetal gestation, anemia, hyperemesis, hemorrhage, and cesarean delivery. The ...