Safely Ruling Out Deep Vein Thrombosis in Pregnancy With the LEFt Clinical Decision Rule and D-Dimer

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.