Venous thromboembolism in pregnancy

Pathophysiology

• Compression of left iliac vein by gravid uterus
  • Most common site is left leg (80%), proximal veins (71%), iliac/femoral veins (64%)

Epidemiology

• Most commonly in post-partum period (up to 6 weeks)

Risk Factors

• Age >35 years
• Obesity
• Prior DVT
• Family history
• Sickle cell disease
• Thrombophilia
• In vitro fertility (IVF) treatments
• Preeclampsia
• Hyperemesis gravidarum
• C-section, especially as emergency

Clinical Presentation

• LEFT clinical prediction tool has a negative predictive value of 100% if all factors are absent
  • Left leg
  • Edema ≥2cm calf circmference difference
  • First trimester presentation

Investigations

• Doppler ultrasound of the extremities is the best initial test
  • Serial ultrasound (three over 6-8 days) has a better negative predictive value
• If ultrasound negative but DVT suspicion is high, need iliac vessel imaging
• If ultrasound negative but PE suspicion is high
  • Chest X-ray, followed by perfusion scan (without ventilation scan)
• D-dimer not as useful
  • Increase as pregnancy progresses (only 1% normal D-dimer in third trimester)
• Bloodwork
  • Only do thrombophilia screen if a significant family history or clot is at an unusual site

Approach to Diagnosis

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Management

• Anticoagulation
  • If attempting to get pregnant: warfarin, then switch to LMWH when pregnant
  • In pregnancy: UFH or LMWH (not warfarin or DOACs)
    • Daily dosing may be equivalent to twice daily dosing in pregnancy
  • While breastfeeding: UFH, LMWH, or warfarin (not DOACs)
  • Duration is 3 months including 6 weeks postpartum interval (which is highest risk period)
• Only consider an IVC filter if they have an absolute contraindication to anticoagulation

Prognosis

• High morbidity and mortality
• Represents about 15% of maternal mortality

Further Reading

• SOGC 2014 Guidelines on Venous Thromboembolism and Antithrombotic Therapy in Pregnancy