This is prospective cohort study in pregnant women who present with signs and symptoms of possible deep vein thrombosis (DVT). All patients will have the same method of assessment of their DVT symptoms (the LEFt clinical decision rule will be applied and D-dimer test will be done) to determine if a compression ultrasound is required. All patients will be followed for a period of 3 months.

VTE is a leading cause of maternal death in the developed world. Suspected DVT in pregnancy is a common clinical problem faced by clinicians daily. The only validated method to exclude DVT in pregnancy requires leg vein CUS imaging. This imaging modality is costly and has limited availability (only available in radiology departments and, usually, only during weekday daytime hours) often necessitating referral to the emergency room for initiation of heparin injections until leg vein CUS can be obtained. A simple and seemingly powerful clinical decision rule (LEFt) and a simple blood test (D-dimer) may be promising to exclude DVT in pregnancy without the need for diagnostic imaging. Validating the safety of a simple, non-invasive, widely available approach to suspected DVT in pregnancy would be an important advance in maternal health.

A prospective cohort diagnostic management study in pregnant women with suspected DVT, with three-month follow-up for symptomatic VTE will take place in multiple centres throughout Canada and Europe.

After obtaining informed consent, all patient will have the LEFt clinical decision rule applied by the attending physician and will have D-Dimer testing (D-Dimer results of test performed within 24 hours will be accepted and do not need to be repeated).

Patients with an "unlikely" LEFt score of 0 or 1 point and a negative D-dimer will not undergo diagnostic imaging.

Patients with either a "likely" LEFt score of 2 or 3 points or a positive D-dimer will undergo either a single complete leg vein compression ultrasound (CCUS) (Day 1) or a serial proximal leg vein (CUS) (Day 1 and Day 7).

All patients will be followed for 3 months for symptomatic VTE.

Inclusion Criteria:

1. Unselected pregnant women (as self-reported by patient and/or previously documented positive beta hCG on urine or serum pregnancy tests) with

2. Suspected acute symptomatic deep vein thrombosis, defined as:

   1. New leg swelling or edema with onset in the last month or,
   2. New leg pain (buttock, groin, thigh or calf) with onset in the last month.

Exclusion Criteria:

1. Below the age of legal consent in jurisdiction of residence (18 years old for Quebec and 16 years old for rest of Canada)
2. Baseline imaging (imaging done after a minimum of 3 months of treatment for prior proximal DVT) not available if suspected recurrence in the same leg as prior
3. Unable or unwilling to provide informed consent
4. Concomitant symptoms of suspected pulmonary embolism (chest pain or shortness of breath or syncope/pre-syncope or unexplained tachycardia)
5. Therapeutic anticoagulant more than 48 hours.

Unselected pregnant women presenting with suspected deep vein thrombosis