Venous thromboembolism (VTE) represents a major cause of morbidity and mortality during pregnancy, complicating from 0.5 to 3.0 of every 1000 pregnancies. Pulmonary embolism (PE) has been the leading cause of maternal mortality in the United States and Great Britain for at least 20 years and complicates approximately 1 in 1,000 pregnancies. This represents a VTE risk of 3–4 times greater than age-matched non-pregnant controls. Diagnosing venous thromboembolism is challenging because clinical findings are often misleading. When evaluated with objective testing, as many as 75% of patients suspected of having venous thromboembolism are found to have an alternative diagnosis. This poses an even greater problem in the pregnant patient who experiences vasodilatation and intravascular volume expansion (20–25% increase) with associated lower extremity edema. The accuracy of many diagnostic tests used in the non-pregnant patient are either not useful at all or are potentially misleading. Diagnosis of VTE is critical since 24% of pregnant women with untreated deep vein thrombosis (DVT) develop PE, with a death rate of 15% to 30%. Proper diagnosis and treatment reduces the mortality rate of PE to 1%–3%. In addition, postphlebitic syndrome in the affected leg occurs nearly 80% of the time following DVT in pregnancy, compared to 30–40% in the non-pregnant patient. Although it is well recognized that the incidence of PE is greatly reduced with treatment for deep vein thrombosis (DVT), treatment is also problematic since anticoagulation regimens used in the non-pregnant patient may be highly teratogenic or in other ways hazardous to mother and/or fetus.