The patient complains of intense and sudden precordial pain, becomes livid in appearance, and presents symptoms of profound dyspnea and eventually of air hunger. These embolisms, however, are not always fatal, a small proportion of the patients recovering. The treatment is purely palliative.
—J. Whitridge Williams (1903)
During the past century, the frequency of venous thromboembolism (VTE) during the puerperium decreased remarkably as early ambulation became more widely practiced. Despite this and other advances in prevention and treatment, however, thromboembolism remains a leading cause of maternal morbidity and mortality. Indeed, thrombotic pulmonary embolism accounted for 9.2 percent of pregnancy-related deaths in the United States between 2011 and 2013 (Creanga, 2017).
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. Deep-vein thrombosis alone is more frequent antepartum, and pulmonary embolism is more common in the first 6 weeks postpartum (Jacobsen, 2008). During 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 (Kamel, 2014).
Rudolf Virchow (1856) postulated that stasis, local trauma to the vessel wall, and hypercoagulability predisposed to venous thrombosis. During normal 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. 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), the synthesis of most clotting factors is markedly enhanced during pregnancy and favors coagulation.
Characteristics for developing thromboembolism during pregnancy are shown in Table 52-1. 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, 2017b). In one study, the magnitude of other risks was estimated from 7177 VTE cases during pregnancy and 7158 events during the postpartum period (James, 2006). Calculated risks for thromboembolism were approximately doubled in women with multifetal gestation, anemia, hyperemesis, hemorrhage, and cesarean delivery. The risk was even greater in pregnancies complicated by postpartum infection. Waldman and associates (2013) found that the risk of VTE was slightly higher in women with advanced maternal age and approximately doubled ...