VTE Risk Score Calculator in Pregnancy (RCOG)

What is VTE and why is pregnancy a risk?

Venous thromboembolism (VTE) is a collective term for deep vein thrombosis (DVT) and pulmonary embolism (PE). During pregnancy and the puerperium, a woman faces a 4- to 5-fold increase in her baseline VTE risk compared with non-pregnant women of the same age. The risk is highest in the first six weeks after delivery. Three overlapping mechanisms explain this: increased clotting-factor levels (particularly fibrinogen and factors VII, VIII and X), venous stasis due to compression of the inferior vena cava and iliac veins by the growing uterus, and endothelial injury during delivery. When a woman also carries identifiable risk factors - such as obesity, thrombophilia, or a prior clot - the cumulative risk rises steeply. The RCOG therefore recommends that every pregnant and postpartum patient be formally risk-assessed with a scored checklist so that thromboprophylaxis is targeted at those who need it most.

How the RCOG scoring system works

The Royal College of Obstetricians and Gynaecologists published its first VTE risk-assessment tool in 2004 and updated it most recently in its Green-top Guideline No. 37a (2015, amended 2023). The tool groups risk factors into three categories. Pre-existing factors are stable background characteristics: a previous VTE, a thrombophilia diagnosis, medical comorbidities, obesity, age over 35, family history, smoking, high parity, and varicose veins. Obstetric factors arise from the current pregnancy: assisted conception, multiple pregnancy, pre-eclampsia, caesarean delivery, operative delivery, prolonged labour, postpartum haemorrhage, preterm birth, and stillbirth. New onset or transient factors can appear at any point: ovarian hyperstimulation syndrome (OHSS), hyperemesis, a surgical procedure, systemic infection, and immobility or dehydration. Each factor carries a score from 1 to 4, reflecting its relative contribution to risk based on observational evidence. The total score is calculated at booking, again at 28 weeks, and at any hospital admission.

Score thresholds and what they mean

For antenatal (antepartum) assessment, a total score of 4 or above triggers a recommendation to consider thromboprophylaxis from the first trimester. A score of exactly 3 triggers a recommendation to start thromboprophylaxis from 28 weeks of gestation, when venous stasis is most pronounced. A score of 2 or below requires no routine pharmacological prophylaxis, though women should receive advice on hydration, avoiding prolonged immobility, and wearing graduated compression stockings if relevant. For postnatal (postpartum) assessment, the threshold is lower: a score of 2 or above after birth indicates that thromboprophylaxis should be considered for at least 10 days. Women with a very high score, or those with a prior VTE, may need prophylaxis for the full six weeks after delivery. The preferred agent in pregnancy and the puerperium is low molecular weight heparin (LMWH), which does not cross the placenta and is compatible with breastfeeding. Warfarin and direct oral anticoagulants are generally avoided antenatally but warfarin may be used postnatally once the mother is no longer breastfeeding or accepts the risks.

Limitations of any scoring tool

The RCOG risk-assessment model was developed from observational data rather than a prospective randomised trial, so its calibration and discrimination are not perfectly established. Studies in populations outside the United Kingdom - including Chinese, South Asian and North American cohorts - have found that the tool performs inconsistently, sometimes failing to separate high- and low-risk groups. It should therefore be treated as a structured aid to clinical judgement, not a replacement for it. Clinicians must review each patient individually, consider factors not captured by the score (such as imminent delivery mode or evolving comorbidities), and apply local hospital protocols. This calculator is designed for educational and reference purposes only, and any patient management decision must involve a qualified healthcare professional.