Deep Vein Thrombosis and Pulmonary Embolus in Pregnancy
Both pregnancy in and the puerperium are described as risk factors for deep vein thrombosis (DVT) and pulmonary embolism (PE); collectively referred to as venous thromboembolic disease. Pregnancy-related blood clot typically occur in the venous system of the lower extremity or in the iliac veins.
- Of venous thromboembolism (VTE) cases: DVT, 80%; PE, 20% (1)
- 1.4 in 1,000 pregnancies, including 1.1 DVT and 0.3 PE in 1,000
- Risk of VTE events is similar in all trimesters.
- Half of all cases occur within the 6-week postpartum period, and thus the risk per day is highest in the weeks following an obstetrical delivery (2).
- In pregnancy, DVT more likely in the left iliofemoral veins as iliac artery (40% increased cardiac output in pregnancy) compresses underlying iliac vein in the vessel’s pelvic course
- Leading cause of maternal death in developed countries—1.1 deaths per 100,000 deliveries
5 times greater risk than in nonpregnant population (1)
Etiology and Pathophysiology
Virchow triad (1)
- Vascular injury: iliac vein injury during delivery
- Venous stasis: progesterone-induced venous dilatation, compression on inferior vena cava (IVC) and iliac veins by gravid uterus
- Hypercoagulability: ↑ coagulation factors (fibrin, factors II/VII/VIII/XI/X, von Willebrand factor [vWF]), ↓ fibrinolytic activity, and free protein S
- History of VTE (15–25% are recurrent cases)
- Inherited or acquired thrombophilias
- High risk: homozygous factor V Leiden (RR:34), homozygous prothrombin G20210A mutation (RR:26), the previous two combined mutation (RR:44) (1)
- Low risk: heterozygous factor V Leiden (RR:8), heterozygous prothrombin G20210A (RR:7), antithrombin III (RR:5) deficiency, protein C (RR:5) or S (RR:3) deficiency. The relative risk is compared to all pregnancies (1); antiphospholipid syndrome (RR is uncertain) (3)
- Age >35 years old
- Obesity (BMI >30), smoking, parity ≥3
- Medical comorbidities: heart and lung disease, SLE, sickle cell, IBD, nephrotic syndrome, T1DM
- Obstetric risk factors include twin (and other multiple gestation), preeclampsia, cesarean section, prolonged labor (>24 hours), operative delivery, severe postpartum hemorrhage.
- Transient and potentially recurring risk factors include assisted reproductive technology (ART), in vitro fertilization (IVF), ovarian hyperstimulation syndrome (OHSS), any surgery during pregnancy, hyperemesis, dehydration, bed rest >3 days, systemic infection, long-distance travel (>4 hours).
Risk of VTE is higher in the postpartum period; interestingly, 2/3 of DVTs happen antepartum and 60% of PEs postpartum. Postpartum incidence of VTE is 10 to 20 times higher than in the nonpregnant state and is especially high after cesarean.
- Screening for thrombophilias even after diagnosis of VTE during pregnancy is not recommended (3)[C].
- Early mobilization, graduated compression stockings for low-risk groups
- Antepartum thromboprophylaxis for high-risk thrombophilia with family history of VTE, ≥2 prior VTE (unprovoked, pregnancy, or estrogen related) (3). If no family history, suggest postpartum prophylaxis for 6 weeks only with prophylactic or intermediate dose low-molecular-weight heparin (LMWH) (3)[B].
- Anticoagulation may not be required if prior VTE was not pregnancy related and associated with a risk factor no longer present.
- Consider thromboprophylaxis for past single episode of idiopathic VTE, low-risk thrombophilia with past VTE, morbid obesity (BMI >40), bedridden patients, and assisted reproduction technologies (3)[C].
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