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Venous Thromboembolism in Pregnancy

In BRIEFING on August 14, 2011 at 3:20 PM

Venous thromboembolism is a life threatening condition that has the unfortunate combination of both increased occurrence and increased difficulty of diagnosis in pregnancy. It is the leading cause of maternal mortality in the developed world (20%), greater than both maternal hemorrhage and pregnancy associated hypertension. As such it is very important to have a high index of suspicion in any pregnant patient seen in the emergency department in distress.

Risk Factors in Pregnancy:
Every pregnant woman is at increased risk of venous thromboembolus due to normal pregnancy changes influencing Virchow’s triad of stasis, hypercoagulability, and endothelial damage.


  • Reduction in venous flow velocity in the legs by 50% by 25-29 weeks
  • IVC compression by gravid uterus
  • Compression of left iliac vein by right iliac artery (70-90% of DVTs found in left leg in the pregnant population!)


  • Fibrin generation ↑, fibrinolytic activity ↓, Coagulation factors II, VII, VIII and X ↑, free protein S ↓, resistance to Protein C.

Endothelial damage

  • Delivery associated with vascular injury and changes at uteroplacental surface.
Signs and Symptoms
Unfortunately, many of the classic signs and symptoms of pulmonary embolism and deep vein thrombosis are very similar to the symptoms of normal pregnancy.  Lower extremity swelling, pain in lower abdomen, tachycardia, tachypnea, and dyspnea can all be found in both normal pregnancy and venous thromboembolus.
So when should we work patients up? 

Predictive Scoring Systems
Unfortunately the Well’s criteria has not been validated in pregnancy and is often unhelpful.
A small pilot study (n=194 pregnant women with 17 documented DVTs) described  the LEFt criteria. (Chan et al. Ann Internal Med 2009)
The LEFt Criteria assigns one point to each of the three following criteria:
  • L: Symptoms in the left leg
  • E: Calf circumference difference ≥ 2 cm
  • Ft: First trimester Presentation
This study demonstrated that risk could be stratified based on number of positive criteria. In the group with 0 points, there were no documented DVTs. In the group with one or more points, there were 16% with documented DVT, and in the group with 2 or 3 points there were 58% documented DVT.
While these results are from a small study, it may be helpful in increasing level of suspicion for further workup.

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