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

Risk Factors

  • 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.

General Prevention

  • 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].
  • DVT prophylaxis both during and following cesarean delivery in the general population may be limited to pneumatic compression devices; however, in morbidly obese women (BMI ≥40), weight-based dosing of enoxaparin should be used postoperatively throughout the remainder of hospitalization (3)[B].

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