16. Thromboembolic Disorders

Summary

Complicating 1 in 1000 to 1 in 2000 pregnancies, venous thromboembolism is a leading cause of maternal morbidity and mortality. Moreover, despite this seemingly low prevalence, pregnancy confers a nearly 6–10-fold increased risk of VTE in women of comparable child-bearing age. In one large retrospective cohort study, 94 of 127 (74.8%) pregnant women with documented deep venous thrombosis developed their clot during the antepartum period, with half detected before 15 weeks and fewer than 30% diagnosed after 20 weeks. In contrast, most cases of pulmonary embolism developed during the postpartum period (23 of 38; 60.5%) and pulmonary embolism was strongly associated with cesarean delivery. However, the per diem risk of venous thromboembolism is approximately threefold to eightfold higher in the puerperium than during an equivalent antepartum interval. Pulmonary embolism is the leading cause of maternal mortality in the US, contributing to 19.6% of such deaths, and translating into 2.3 pregnancy-related deaths per 100,000 livebirths. An untreated deep venous thrombosis presents a 25% risk of pulmonary embolism, with a mortality rate of approximately 15% if undetected and untreated. On the other hand, if a deep venous thrombosis is promptly diagnosed and treated, the risk of pulmonary embolism is less than 5% and the risk of maternal mortality is less than 1%. The increased risk of pregnancy-associated venous thromboembolism reflects local and systemic mechanisms that mitigate the risk of hemorrhage during placentation and the third stage of labor. Appreciation of the thrombotic risk of pregnancy demands knowledge of the sophisticated systems of coagulation and fibrinolysis and their inhibitors.