Estimate venous thromboembolism risk during pregnancy and postpartum using RCOG criteria
| Score | Phase | Recommended action |
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Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.
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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.
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.
Move to Obstetric risk factors. Answer for pre-eclampsia, ART, multiple pregnancy, cesarean type, instrumental delivery, postpartum hemorrhage, preterm birth, and stillbirth.
Finish with the Transient risk factors. Surgery, hyperemesis, OHSS, systemic infection, and immobility sit in this block.
Watch the total score update live as you change inputs. The hero panel shows total, antenatal, and postnatal figures side by side.
Read the recommendation tile. It tells you whether LMWH is indicated and when to start it.
Tap Calculate to force a refresh if you want to be sure the latest inputs are captured.
Use Reset to clear everything back to defaults.
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.
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.
An antenatal score of 4 or higher is high, and triggers LMWH from the first trimester. A score of exactly 3 is moderate and triggers LMWH from 28 weeks. Postnatally, a score of 2 or higher means at least 10 days of LMWH.
The RCOG scoring system is a point-based checklist published in Green-top Guideline No. 37a. Each risk factor carries 1 to 4 points. The total score maps to an action threshold: no treatment, treatment from 28 weeks, or treatment from the first trimester.
Previous VTE carries the most weight. High-risk thrombophilia, medical comorbidities like cancer or heart failure, surgery during pregnancy, hyperemesis, and OHSS also carry heavy weights. Age over 35, BMI over 30, smoking, parity of 3 or more, and varicose veins add smaller contributions.
The calculator adds points for each active risk factor. Some factors count only antenatally, some only postnatally. The total determines whether LMWH is recommended, and when to start it. The thresholds are 4 antenatally and 2 postnatally.
Yes. BMI 30 to 39.9 adds 1 point. BMI 40 or higher adds 2 points. Obesity increases baseline clotting risk and reduces mobility, so it’s one of the more common contributors to a moderate or high score.
An antenatal score of 3 means LMWH is considered starting at 28 weeks. It’s not an emergency. It’s a signal to plan ahead. Your provider will decide whether to start treatment based on your full clinical picture.
No. The scoring system is specific to pregnancy and the postpartum period. Many of the inputs (pre-eclampsia, cesarean type, hyperemesis) only apply during or after a pregnancy. Using it outside that context would give meaningless results.
Yes. LMWH doesn’t cross the placenta, so it doesn’t reach the fetus. It’s the standard anticoagulant for pregnancy and breastfeeding. Unlike warfarin, it doesn’t cause fetal harm. Some women get bruising at the injection site, but serious side effects are uncommon.
The RCOG recommends reassessment at booking, at 28 weeks, on any hospital admission, during labor, and before postnatal discharge. Risk factors change as pregnancy progresses, so a single score at booking isn’t enough.
Antenatal VTE risk refers to the pregnancy itself. Postnatal risk covers the six weeks after delivery, which carry the highest absolute clot risk. Some factors apply in both phases. Others, like cesarean type and postpartum hemorrhage, apply only postnatally.
Usually yes, but timing matters. LMWH must be paused before an epidural or spinal to reduce bleeding risk. The exact window depends on dose, prophylactic doses are typically paused 12 hours before, therapeutic doses 24 hours. Your anesthesiologist will confirm.
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