Pregnancy imparts a four fold to five fold increased risk of thromboembolism when compared to the nonpregnant state.1 This risk rises to a 20-fold increase during the postpartum period and does not return to nonpregnant levels until approximately 6 weeks’ postpartum.1,2 The majority of thromboembolic events in pregnancy are venous in origin. The incidence of venous thromboembolism (VTE) in pregnant women is estimated to be 5 to 12 events per 10,000 pregnancies, evenly distributed between the time period from conception to delivery.1 The mortality from pregnancy related VTE is 1.1 deaths per 100,000, an estimate of about 10% of all maternal deaths.3
Types of Venous Thromboembolism
Venous thromboembolism in pregnancy is commonly manifested as pulmonary embolism or as deep venous thrombosis (DVT). DVT accounts for 80% of thromboembolic cases, while pulmonary embolism is responsible for the remaining 20%.4
Pulmonary embolism (PE) is the leading cause of direct maternal deaths in developed countries, and it accounts for 20% of pregnancy-related deaths.3 The incidence of PE is 0.01% to 0.05% of all pregnancies, and the risk is greater in the postpartum period, with 43% to 60% of pregnancy-related episodes occurring 4 to 6 weeks postpartum. PE after cesarean delivery is higher than after vaginal delivery by a factor of 2.5 to 20, and the incidence of fatal PE is higher by a factor of 10.2
The incidence of DVT is 0.02% to 0.36% of all pregnancies. A meta-analysis showed that two-thirds of cases of DVT occur antepartum and are equally distributed across trimesters.5 Pregnancy-associated DVT is left sided in more than 85% of cases. The mechanism for this predilection for the left leg is probably related to compression of the left iliac vein by the right iliac artery and the gravid uterus (Figure 19-1).1
Mechanism for predilection for left leg deep venous thrombosis likely related to compression of the left iliac vein by the right iliac artery and the gravid uterus. (From Bourjeily G, Paidas M, Khalil H.1, with permission.)
Isolated pelvic vein thrombosis (PVT) is more common in pregnancy. According to a multicenter prospective registry, 11% (6 of 53) of pregnant or postpartum women with DVT had isolated PVT compared with 1% (17 of 5451) of nonpregnant patients.1 Ovarian vein thrombosis, a form of septic PVT, may complicate less than 0.05% of vaginal deliveries and up to 1% to 2% of cesarean deliveries. In 90% of cases, PVT occurs within 10 days’ postpartum but can occur up to 10 weeks’ postpartum. Symptoms include fever ...