Gravid VTE Exclusion Pathway v2.0LEFt Rule & Pregnancy-Adapted YEARS Algorithm
📈 Gravid Patient Protocol: Standard VTE algorithms (Wells', PERC) are invalidated by pregnancy. This pathway strictly utilises the LEFt rule for suspected DVT and the Pregnancy-Adapted YEARS algorithm for suspected PE to minimise unnecessary foetal and maternal radiation.
1 Suspected Pathology
2 The LEFt Clinical Criteria
2 The Pregnancy-Adapted YEARS Criteria
ng/mL (or μg/L) FEU
⚠ Assay Unit Check: Ensure the lab assay reports in Fibrinogen Equivalent Units (FEU). If the lab reports in D-Dimer Units (DDU), you must multiply the DDU value by 2 before entering it here (e.g., 250 DDU = 500 FEU).
Assessment Score
📚 Pathway Architecture & Clinical Application1. The LEFt Rule for DVT
The LEFt rule is a highly validated pre-test probability score specifically for pregnant women. It evaluates three parameters: Left leg presentation (due to physiological compression of the left iliac vein by the gravid uterus and right iliac artery), Edema (calf circumference difference ≥ 2 cm), and First trimester presentation. A score of 0 indicates a low probability of DVT, allowing for safe exclusion if combined with a negative D-dimer.
2. The Pregnancy-Adapted YEARS Algorithm for PE
D-Dimer levels naturally and progressively rise during a normal pregnancy, making the standard 500 ng/mL cut-off virtually useless in the second and third trimesters (leading to extreme false-positive rates and unnecessary CT scans). The YEARS algorithm establishes dynamic, criteria-based D-Dimer thresholds:
If 0 YEARS criteria are met: The safe D-Dimer threshold is raised to 1000 ng/mL.
If 1 to 3 YEARS criteria are met: The threshold remains at 500 ng/mL.
If Clinical signs of DVT are present: A Compression Ultrasound (CUS) is mandated first to confirm VTE without radiation. D-Dimer is only used if the CUS is negative.
Pharmacological Management in Pregnancy
⚠ Absolute Contraindications Direct Oral Anticoagulants (DOACs) (e.g., Apixaban, Rivaroxaban) cross the placenta and are strictly contraindicated in pregnancy due to reproductive toxicity and foetal bleeding risks. Warfarin is teratogenic (warfarin embryopathy) and is generally contraindicated, especially in the first trimester.
💊 Standard of Care: LMWH Low Molecular Weight Heparin (LMWH) (e.g., Enoxaparin) is the anticoagulant of choice during pregnancy. It does not cross the placental barrier and is not secreted into breast milk. Dosing must be actively adjusted as maternal weight and renal clearance dynamically increase throughout the trimesters.
⚠ Clinical Disclaimer: These algorithms are clinical decision aids. The YEARS algorithm significantly reduces the need for CTPA in pregnant women. However, if clinical suspicion remains severe despite a negative algorithmic result, further imaging, V/Q scanning, or specialist consultation is mandated.
Gravid VTE Exclusion Pathway — Clinical decision support for educational purposes. Unauthorised reproduction, redistribution, or modification of this tool is prohibited. For permissions, contact mediscuss.org/contact.
Algorithm References & Evidence Base
Bistervels IM, et al. Pregnancy-Adapted YEARS Algorithm for Diagnosis of Suspected Pulmonary Embolism. N Engl J Med. 2019.
Righini M, et al. Clinical prediction rules for the diagnosis of deep vein thrombosis in pregnancy: The LEFt rule. Ann Intern Med. 2013.
Bates SM, et al. VTE, Thrombophilia, Antithrombotic Therapy, and Pregnancy: Antithrombotic Therapy and Prevention of Thrombosis. Chest. 2012.
