Assess venous thromboembolism (VTE) risk during pregnancy and postpartum. Score 20 risk factors with odds ratios, stage-specific multipliers, and prophylaxis effects.
Venous thromboembolism (VTE) — encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE) — remains one of the leading causes of maternal mortality in developed countries. Pregnancy increases VTE risk 4–5 fold through Virchow's triad: hypercoagulability from increased clotting factors, venous stasis from uterine compression, and potential endothelial injury during delivery.
This VTE Risk in Pregnancy Calculator incorporates 20 evidence-based risk factors with published odds ratios, stage-specific risk multipliers from first trimester through 6 weeks postpartum, and the protective effect of current thromboprophylaxis. The tool combines these factors to estimate personalized VTE risk and provide guideline-based management suggestions.
Risk assessment should be performed at booking, during pregnancy if risk factors change, and again at delivery. Postpartum VTE risk is approximately 2.5 times higher than antenatal risk, making post-delivery assessment particularly important. This calculator supports clinical decision-making alongside professional guidelines from RCOG, ACOG, and other national bodies.
Use the preset examples to load common values instantly, or type in custom inputs to see results in real time. The output updates as you type, making it practical to compare different scenarios without resetting the page.
VTE is preventable with appropriate thromboprophylaxis but remains a leading cause of maternal death. This calculator helps healthcare providers systematically assess risk factors, identify high-risk patients, and make evidence-based decisions about LMWH prophylaxis. It is also a valuable educational tool for understanding how multiple risk factors compound pregnancy VTE risk.
Adjusted Risk = Baseline Risk (1.2/1000) × Product of Selected ORs × Stage Multiplier × Prophylaxis Factor Stage Multipliers: T1=0.6, T2=0.8, T3=1.2, Postpartum=2.5 Prophylaxis: LMWH prophylactic=70% reduction, LMWH treatment=85%, Compression=30%
Result: Very High Risk: 72.6 per 1,000 (7.3%)
Previous VTE (OR 24.8) × BMI ≥ 30 (OR 2.7) × Caesarean (OR 3.6) × Postpartum (×2.5) = combined risk 72.6/1,000. Prophylactic LMWH strongly recommended.
VTE risk in pregnancy is cumulative and multiplicative. A woman with no additional risk factors has approximately 1.2 per 1,000 baseline risk across pregnancy. Adding a single major factor like previous VTE (OR 24.8) raises this dramatically. When multiple factors coexist — as commonly occurs with obesity, advanced maternal age, and caesarean delivery — the compounding effect can push risk into very high territory.
The risk factors in this calculator are drawn from large epidemiological studies, meta-analyses, and clinical guidelines from RCOG, ACOG, and SOMANZ. Each odds ratio represents the average relative risk increase associated with that factor across published literature.
Low-molecular-weight heparin (LMWH) — typically enoxaparin or dalteparin — is the cornerstone of pregnancy thromboprophylaxis. Prophylactic doses (e.g., enoxaparin 40mg daily) are typically prescribed for moderate to high-risk patients, while treatment doses are reserved for acute VTE or very high-risk scenarios.
The timing and duration of prophylaxis depend on the risk profile: some patients require LMWH from the first trimester through 6 weeks postpartum, while others may need it only postpartum. Graduated compression stockings complement pharmacological prophylaxis, particularly during prolonged immobilization or long-haul travel.
The postpartum period, especially the first 1–2 weeks after delivery, represents the highest risk window. The combination of delivery-related endothelial injury, immobilization during recovery, and persistent hypercoagulability creates a perfect storm for thrombosis. Emergency caesarean section further amplifies this risk. Postpartum VTE assessment and appropriate prophylaxis are critical interventions that can prevent maternal death from pulmonary embolism.
The baseline risk is approximately 1–2 per 1,000 pregnancies, which is 4–5 times higher than in non-pregnant women of the same age. Risk is highest in the postpartum period, particularly the first 6 weeks after delivery.
Virchow's triad describes the three factors predisposing to thrombosis: (1) hypercoagulability — pregnancy increases fibrinogen, factors VII, VIII, X, and von Willebrand factor; (2) venous stasis — the gravid uterus compresses the IVC and pelvic veins; (3) endothelial injury — possible during delivery, especially caesarean section. Understanding this concept helps you apply the calculator correctly and interpret the results with confidence.
Per RCOG Green-top Guideline 37a, assess at booking, at each admission, during significant illness or immobilization, following delivery, and whenever risk factors change. Many institutions also assess each trimester.
Yes. Low-molecular-weight heparin (LMWH) is the anticoagulant of choice in pregnancy. It does not cross the placenta, has a predictable dose-response, and has an excellent safety profile for both mother and fetus.
Warfarin crosses the placenta and is teratogenic, especially in the first trimester (warfarin embryopathy). It is contraindicated in pregnancy except in specific circumstances like mechanical heart valves, and only in the second trimester.
The RCOG guideline uses a point-based scoring system. This calculator uses odds ratios for a more granular risk estimate. Both approaches identify high-risk patients for thromboprophylaxis. Clinical guidelines should always take precedence.
Routine screening is not recommended. Testing is typically performed after unprovoked VTE, recurrent pregnancy loss, or strong family history. The thrombophilia reference table in this calculator lists conditions and screening indications.