The increased risk of VTE in pregnancy is mediated through normal physiologic changes (Figure 1), including alterations in hemostasis that favor coagulation (decreased levels of free protein S and increased levels of fibrinogen, factors VII and VIII, and von Willebrand factor), reduced fibrinolysis (due to increased synthesis of plasminogen activator inhibitors 1 and 2) and stasis of blood in the lower limbs (as a result of hormone-induced venodilation, compression of the pelvic veins by the gravid uterus and compression of the left iliac vein by the right iliac artery).[7,13,14] Thrombophilia, prior VTE, smoking, obesity, immobility, assisted reproduction and postpartum factors such as infection and bleeding also increase the risk of pregnancy-related VTE.[7,8,15]
Causes of increased risk of venous thromboembolism in pregnancy. The hemostatic and mechanical changes in pregnancy that contribute to the increased risk of venous thromboembolism are shown.Data taken from [7,13–15].
Studies in which either all or most patients underwent accurate diagnostic testing for VTE report an incidence that ranges from 0.6 to 1.7 episodes per 1000 deliveries.[1–6] Although these rates are low, they represent a five- to 15-fold increase in risk compared with those reported for nonpregnant women of comparable age. Eighty five percent of all pregnancy-related symptomatic events are deep vein thrombosis (DVT). Roughly two-thirds of all DVT occur antepartum, with half of these events occurring before the third trimester. By contrast, pulmonary embolism (PE) is relatively less frequent during pregnancy but more frequent than DVT postpartum.[1,2] PE remains one of the leading causes of direct maternal mortality in developed countries.[17,18] Regardless of the type of event, the daily risk of VTE is considerably higher following delivery than antepartum. Compared with age-matched nonpregnant women, the daily risk of VTE is increased five-to tenfold during the antepartum period and 15- to 35-fold after delivery. The elevated risk of VTE following delivery returns to baseline by the end of the sixth postpartum week.
Expert Rev Hematol. 2013;6(3):287-300. © 2013 Expert Reviews Ltd.