Assessment result
Results will appear here after you tick the risk factors above.
Weight-based prophylactic LMWH dose table
Enter your body weight to highlight the matching dose row. This table is purely an educational reference — actual doses are determined only by a doctor.
Frequently asked questions (FAQ)
What is VTE and why does pregnancy increase its risk?
VTE (venous thromboembolism) is a blood clot in the veins, covering DVT (deep vein thrombosis, a clot in a deep vein, usually in the leg) and PE (pulmonary embolism, a clot blocking a lung vessel). Pregnancy increases the risk through three changes: blood clots more easily, venous blood flow slows, and return vessels are compressed by the enlarging uterus. The highest risk occurs in the first weeks after delivery.
What is the difference between antenatal and postnatal VTE risk assessment?
Antenatal assessment is done during pregnancy with thresholds: score ≥ 4 → consider prophylaxis from the first trimester; score 3 → consider from 28 weeks of gestation. Postnatal assessment is done after delivery with thresholds: score ≥ 2 → consider at least 10 days of prophylaxis; high-risk profile → 6 weeks. Some factors are scored in one phase only — e.g. ART/IVF is antenatal only, while caesarean delivery type is postnatal only.
How do I calculate my risk score with this tool?
Select the Antenatal (during pregnancy) or Postnatal (after delivery) tab, then tick each risk factor that applies. Each factor carries a weight of 1–4 per RCOG Green-top Guideline No. 37a Appendix III (e.g. VTE history = 4, emergency caesarean = 2, age > 35 years = 1). The score is summed automatically and grouped into low, intermediate, or high risk with an explanation of follow-up.
When is LMWH prophylaxis started and stopped per RCOG?
Per RCOG Green-top 37a: antenatal score ≥ 4 → consider LMWH from the first trimester; score 3 → consider from 28 weeks of gestation. Postnatal score ≥ 2 → consider LMWH for at least 10 days after delivery; high-risk profile (VTE history, high-risk thrombophilia, or antenatal LMWH) → 6 weeks. Actual schedules and doses are determined only by a doctor.
Who should not receive LMWH prophylaxis?
RCOG lists conditions that are contraindications or need special caution: inherited bleeding disorders (e.g. haemophilia or von Willebrand disease), active bleeding, major bleeding risk (e.g. placenta praevia), platelets below 75 × 10⁹/L, stroke within the last 4 weeks, severe renal impairment (GFR < 30), severe hepatic impairment, and uncontrolled hypertension (> 200/120 mmHg). If any of these apply, the balance of bleeding and thrombosis risk must be discussed with a doctor.
Does this calculator replace a doctor’s or midwife’s assessment?
No. This tool is an educational aid based on the RCOG Green-top 37a checklist and is not medical advice. Clinical assessment considers many things not covered by the checklist, including full history, physical examination, and laboratory results. Always discuss any results from this tool with your doctor or midwife.
I have a previous VTE — how is it managed?
Per RCOG, a previous VTE (except a single event provoked by major surgery with no other risk factors) places the mother at high risk: LMWH prophylaxis is recommended throughout pregnancy and for 6 weeks after delivery. Consult early in pregnancy (ideally before conceiving) with a doctor or clinic experienced in pregnancy thrombosis.
What is the difference between high-risk and low-risk thrombophilia?
High-risk thrombophilia per RCOG includes antithrombin deficiency, protein C or S deficiency, and antiphospholipid syndrome — requiring specialist management and usually higher-dose prophylaxis. Low-risk thrombophilia is heterozygous Factor V Leiden or prothrombin gene mutation without VTE history — counted as a single risk factor (score 1) in the assessment.
When should VTE risk assessment be repeated?
RCOG advises VTE risk assessment ideally before pregnancy or in early pregnancy, repeated whenever the mother is admitted to hospital or develops a new problem during pregnancy, and repeated again at delivery or soon after birth. Risk factors can appear or resolve as pregnancy progresses.
What should I do if my result is low risk?
For low risk, RCOG’s general advice is mobilisation (staying active as your doctor advises) and avoiding dehydration. Know the symptoms of DVT (pain/swelling in one leg, redness, warmth) and PE (sudden breathlessness, chest pain, coughing blood) — seek medical help immediately if they appear. Repeat the assessment if your situation changes, e.g. prolonged bed rest or hospital admission.
Related calculators
- Padua Score — VTE risk in medical inpatients
- 4Ts Score — HIT (heparin-induced thrombocytopenia) probability
- Age-adjusted D-dimer cutoff to rule out VTE
- All calculators directory
- nrtechstudio home
Scope note: the Padua Score validates VTE risk in medical inpatients and explicitly excludes pregnant women; this tool (RCOG 37a) is specifically for pregnancy and the puerperium. They are different instruments — do not mix them.
Sources & attribution
- Royal College of Obstetricians and Gynaecologists. Reducing the Risk of Venous Thromboembolism during Pregnancy and the Puerperium, Green-top Guideline No. 37a (April 2015, amended 2023). Scoring system: Appendix III; LMWH dose table: Table 3; contraindications: Appendix III.
- The primary document is published open-access by RCOG (rcog.org.uk). All factor weights, stratification thresholds, and doses in this tool were verified directly against that primary document, not secondary sites.