Pregnancy raises the risk of deep vein thrombosis and pulmonary embolism four- to six-fold, and the risk is highest in the weeks after birth. RCOG Green-top Guideline 37a uses a points score to decide who should receive low-molecular-weight heparin (LMWH).
How to use the VTE Risk in Pregnancy Calculator
- Previous VTE (not related to major surgery)
- Previous VTE related to major surgery
- Known high-risk thrombophilia
- Medical comorbidity (cancer, heart failure, lupus, IBD, nephrotic syndrome, sickle cell, IV drug use)
- Family history of unprovoked or oestrogen-related VTE in a first-degree relative
- Known low-risk thrombophilia (no VTE)
- Age over 35
- Parity 3 or more
- Smoker
- Gross varicose veins
- Current pre-eclampsia
- Conceived with ART/IVF (antenatal only)
- Multiple pregnancy
- Surgery in pregnancy or after birth
- Hyperemesis
- OHSS (first trimester only)
- Admission to hospital or immobility (3+ days)
- Current systemic infection
- Dehydration
- Caesarean section in labour (after birth)
- Elective caesarean section (after birth)
- Mid-cavity or rotational operative delivery (after birth)
- Prolonged labour (over 24 h) (after birth)
- Postpartum haemorrhage over 1 litre or transfusion (after birth)
- Preterm birth before 37 weeks this pregnancy (after birth)
- Stillbirth this pregnancy (after birth)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Each answer carries the points shown in the published score. The calculator adds them up and maps the total to the published interpretation.
Scoring table
| Item | Answers and points |
|---|---|
| Previous VTE (not related to major surgery) | No = 0; Yes = 4 |
| Previous VTE related to major surgery | No = 0; Yes = 3 |
| Known high-risk thrombophilia | No = 0; Yes = 3 |
| Medical comorbidity (cancer, heart failure, lupus, IBD, nephrotic syndrome, sickle cell, IV drug use) | No = 0; Yes = 3 |
| Family history of unprovoked or oestrogen-related VTE in a first-degree relative | No = 0; Yes = 1 |
| Known low-risk thrombophilia (no VTE) | No = 0; Yes = 1 |
| Age over 35 | No = 0; Yes = 1 |
| Parity 3 or more | No = 0; Yes = 1 |
| Smoker | No = 0; Yes = 1 |
| Gross varicose veins | No = 0; Yes = 1 |
| Current pre-eclampsia | No = 0; Yes = 1 |
| Conceived with ART/IVF (antenatal only) | No = 0; Yes = 1 |
| Multiple pregnancy | No = 0; Yes = 1 |
| Surgery in pregnancy or after birth | No = 0; Yes = 3 |
| Hyperemesis | No = 0; Yes = 3 |
| OHSS (first trimester only) | No = 0; Yes = 4 |
| Admission to hospital or immobility (3+ days) | No = 0; Yes = 1 |
| Current systemic infection | No = 0; Yes = 1 |
| Dehydration | No = 0; Yes = 1 |
| Caesarean section in labour (after birth) | No = 0; Yes = 2 |
| Elective caesarean section (after birth) | No = 0; Yes = 1 |
| Mid-cavity or rotational operative delivery (after birth) | No = 0; Yes = 1 |
| Prolonged labour (over 24 h) (after birth) | No = 0; Yes = 1 |
| Postpartum haemorrhage over 1 litre or transfusion (after birth) | No = 0; Yes = 1 |
| Preterm birth before 37 weeks this pregnancy (after birth) | No = 0; Yes = 1 |
| Stillbirth this pregnancy (after birth) | No = 0; Yes = 1 |
Inputs explained
| Field | What to enter |
|---|---|
| Previous VTE (not related to major surgery) | Choose one: No, Yes |
| Previous VTE related to major surgery | Choose one: No, Yes |
| Known high-risk thrombophilia | Choose one: No, Yes |
| Medical comorbidity (cancer, heart failure, lupus, IBD, nephrotic syndrome, sickle cell, IV drug use) | Choose one: No, Yes |
| Family history of unprovoked or oestrogen-related VTE in a first-degree relative | Choose one: No, Yes |
| Known low-risk thrombophilia (no VTE) | Choose one: No, Yes |
| Age over 35 | Choose one: No, Yes |
| Parity 3 or more | Choose one: No, Yes |
| Smoker | Choose one: No, Yes |
| Gross varicose veins | Choose one: No, Yes |
| Current pre-eclampsia | Choose one: No, Yes |
| Conceived with ART/IVF (antenatal only) | Choose one: No, Yes |
| Multiple pregnancy | Choose one: No, Yes |
| Surgery in pregnancy or after birth | Choose one: No, Yes |
| Hyperemesis | Choose one: No, Yes |
| OHSS (first trimester only) | Choose one: No, Yes |
| Admission to hospital or immobility (3+ days) | Choose one: No, Yes |
| Current systemic infection | Choose one: No, Yes |
| Dehydration | Choose one: No, Yes |
| Caesarean section in labour (after birth) | Choose one: No, Yes |
| Elective caesarean section (after birth) | Choose one: No, Yes |
| Mid-cavity or rotational operative delivery (after birth) | Choose one: No, Yes |
| Prolonged labour (over 24 h) (after birth) | Choose one: No, Yes |
| Postpartum haemorrhage over 1 litre or transfusion (after birth) | Choose one: No, Yes |
| Preterm birth before 37 weeks this pregnancy (after birth) | Choose one: No, Yes |
| Stillbirth this pregnancy (after birth) | Choose one: No, Yes |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Score = sum of the points for each item
Worked example
Inputs — Previous VTE (not related to major surgery): No; Previous VTE related to major surgery: No; Known high-risk thrombophilia: No; Medical comorbidity (cancer, heart failure, lupus, IBD, nephrotic syndrome, sickle cell, IV drug use): No; Family history of unprovoked or oestrogen-related VTE in a first-degree relative: No; Known low-risk thrombophilia (no VTE): No; Age over 35: No; Parity 3 or more: No; Smoker: No; Gross varicose veins: No; Current pre-eclampsia: No; Conceived with ART/IVF (antenatal only): No; Multiple pregnancy: No; Surgery in pregnancy or after birth: No; Hyperemesis: No; OHSS (first trimester only): No; Admission to hospital or immobility (3+ days): No; Current systemic infection: No; Dehydration: No; Caesarean section in labour (after birth): No; Elective caesarean section (after birth): No; Mid-cavity or rotational operative delivery (after birth): No; Prolonged labour (over 24 h) (after birth): No; Postpartum haemorrhage over 1 litre or transfusion (after birth): No; Preterm birth before 37 weeks this pregnancy (after birth): No; Stillbirth this pregnancy (after birth): No.
Results — Antenatal score = 0 points; Postnatal score = 0 points; Antenatal recommendation = Mobilise and avoid dehydration; Postnatal recommendation = Early mobilisation and avoid dehydration.
Key terms
- VTE
- Venous thromboembolism.
- LMWH
- Low-molecular-weight heparin.
Frequently asked questions
When is the risk of blood clots highest?
In the first six weeks after birth, especially after a caesarean.
What is LMWH?
Low-molecular-weight heparin, a blood thinner given by injection that is safe in pregnancy and breastfeeding.
What symptoms should I watch for?
Pain or swelling in one leg, sudden breathlessness or chest pain – seek urgent care.