VTE Risk Score Calculator in Pregnancy

Introduction

Blood clots kill more pregnant women in the UK than any other single cause. That’s the reason the RCOG built its risk-scoring system. Rather than relying on clinical intuition alone, the score turns 23 weighted risk factors into a number and pairs that number with a clear action threshold. This VTE risk score calculator reproduces that system. It’s built for obstetricians, midwives, and pregnant patients who want a structured estimate before a formal assessment. The tool scores each factor, splits the total between the antenatal and postnatal phases, and outputs a recommendation that mirrors RCOG Green-top Guideline No. 37a. A patient with a BMI of 42 and a prior provoked VTE will get a different recommendation than one with a BMI of 32 and no history. That’s the point. The output gives you something concrete to bring to the next appointment.

How to Use the VTE Risk Score Calculator in Pregnancy

1. Work through the Pre-existing risk factors section first. Previous VTE, thrombophilia type, medical comorbidities, family history, age, BMI, parity, smoking, and varicose veins all live here.

2. Move to Obstetric risk factors. Answer for pre-eclampsia, ART, multiple pregnancy, cesarean type, instrumental delivery, postpartum hemorrhage, preterm birth, and stillbirth.

3. Finish with the Transient risk factors. Surgery, hyperemesis, OHSS, systemic infection, and immobility sit in this block.

4. Watch the total score update live as you change inputs. The hero panel shows total, antenatal, and postnatal figures side by side.

5. Read the recommendation tile. It tells you whether LMWH is indicated and when to start it.

6. Tap Calculate to force a refresh if you want to be sure the latest inputs are captured.

7. Use Reset to clear everything back to defaults.

How the VTE Risk Score Formula Works

The calculator uses a point-based additive model. Each risk factor carries a fixed weight between 1 and 4 points. Add them up, and the total determines the recommendation. No multiplication, no logistic regression. It’s a checklist with weights.

Formula: Total score = Σ (points for each active risk factor)

The heaviest factors are previous VTE not related to surgery (4 points) and OHSS (4 points). Previous surgery-provoked VTE, high-risk thrombophilia, medical comorbidities, surgery in pregnancy, and hyperemesis each carry 3 points. Age over 35, BMI 30 to 39.9, parity of 3 or more, smoking, varicose veins, pre-eclampsia, ART, multiple pregnancy, systemic infection, and immobility all contribute 1 point each. BMI 40 or higher gives 2 points instead of 1. Cesarean in labor gives 2 points. Elective cesarean gives 1.

The trick is that not every factor counts in every phase. ART and hyperemesis apply antenatally only. Cesarean type, instrumental delivery, prolonged labor, PPH, preterm birth, and stillbirth apply postnatally only. A few factors (surgery, for example) sit in both columns. That’s why the tool shows two separate scores.

The antenatal threshold is 4 points or higher for starting LMWH in the first trimester, or exactly 3 points for starting at 28 weeks. The postnatal threshold is 2 points or higher for at least 10 days of LMWH. Below those thresholds, routine care with reassessment is the recommendation.

Worked Example

A 38-year-old woman at 12 weeks. BMI is 33. She had a provoked DVT after knee surgery five years ago. No thrombophilia. No medical comorbidities. No family history. Para 2. Non-smoker. No varicose veins.

Pre-existing points: age over 35 (1) + BMI 33 (1) + prior surgery-provoked VTE (3) = 5 points. That’s already over the first-trimester threshold of 4.

Add in obstetric and transient factors. No pre-eclampsia, no ART, no multiple pregnancy. No surgery, no hyperemesis, no OHSS, no infection, no immobility. Total: 5 points.

Antenatal score: 5. Postnatal score would be the same 5 (all her factors persist into the postnatal phase). The recommendation reads: consider LMWH from the first trimester. The category label shows High (antenatal). The verdict banner turns red.

Now change one input. Drop her BMI to 28. Age over 35 still gives 1, prior VTE still gives 3. Total = 4. Still above the first-trimester threshold, but only just. The same recommendation applies, but with a narrower margin.

Drop her age to 34 as well. Now the total is 3. That moves her into the Moderate category. The recommendation shifts to “consider LMWH from 28 weeks” instead of the first trimester. Two small input changes moved her from a first-trimester start to a third-trimester start.