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During the past century, the frequency of venous thromboembolism (VTE) during the puerperium decreased remarkably as early ambulation became routine practice. Despite this and other advances in prevention and treatment, thromboembolism remains a leading cause of maternal morbidity and mortality (Abe, 2019). Thrombotic pulmonary embolism accounted for almost 10 percent of pregnancy-related deaths in the United States between 2011 and 2015 (Creanga, 2017; Petersen, 2019).

The absolute incidence of VTE during pregnancy is low—1 or 2 cases per 1000 pregnancies. However, the risk is approximately five times higher than that among women who are not pregnant (Greer, 2015). Approximately equal numbers of cases are identified antepartum and in the puerperium. But deep-vein thrombosis alone is more frequent antepartum, and pulmonary embolism is more common postpartum. During the first 6 weeks of the puerperium, the estimated incidence of a thromboembolic complication is 22 events per 100,000 deliveries. Although still elevated, the risk falls to approximately 3 cases per 100,000 deliveries during the second 6-week postpartum period (Kamei, 2014). As many as 2 percent of these women have postthrombotic syndrome (Govindappagari, 2020).

PATHOPHYSIOLOGY

Rudolf Virchow (1856) postulated that stasis, local trauma to the vessel wall, and hypercoagulability predisposed to venous thrombosis. During pregnancy, the risk for each of these rises. Compression of the pelvic veins and inferior vena cava by the enlarging uterus renders the lower extremity venous system particularly vulnerable to stasis. 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, delivery, preeclampsia, and sepsis contribute to endothelial cell injury. Last, as listed in the Appendix (p. 1228), the synthesis of most clotting factors is markedly enhanced during pregnancy and favors coagulation.

Risk factors for developing VTE during pregnancy are shown in Table 55-1. The most important of these is a personal history of thrombosis. Specifically, 15 to 25 percent of all VTE cases during pregnancy are recurrent events (American College of Obstetricians and Gynecologists, 2020b). Another important individual risk factor is a genetically determined thrombophilia. An estimated 20 to 50 percent of women who develop a venous thrombosis during pregnancy or postpartum have an identifiable underlying procoagulant genetic disorder (American College of Obstetricians and Gynecologists, 2020a).

TABLE 55-1Some Risk Factors Associated with an Increased Risk for VTE

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