RCOG 37a — thromboembolic risk in pregnancy

Interactive tool

VTE risk assessment and indicative recommendation on thromboprophylaxis

First state whether the assessment is antenatal or postpartum: some items count only in one of the two phases. Age and BMI are converted into points automatically from the patient data, without having to tick them separately.

Result

Summary of factors and text for the report

How to use it

Instructions

When it applies

The scoring system is designed to be applied at booking, at every admission, at every relevant clinical change and immediately after delivery. It is not a one-off assessment: the score at the first visit almost always underestimates the risk in the third trimester and the puerperium.

Antenatal or postpartum

The two assessments use the same table but different thresholds, and some items are relevant to one phase only:

• Assisted reproductive technology and ovarian hyperstimulation syndrome are antenatal items; hyperstimulation, in particular, applies to the first trimester only.
• Mode of delivery, prolonged labour, postpartum haemorrhage, preterm birth and stillbirth enter the calculation only in the postpartum assessment. If they are ticked in the antenatal phase, the calculator flags them and does not count them.

Items that do not add up

• BMI: 1 point for BMI between 30 and 39, 2 points for BMI of 40 or more. The two bands are not cumulative; the calculator applies only the higher one.
• Mode of delivery: caesarean section in labour (2 points), elective caesarean section (1 point) and mid-cavity or rotational operative delivery (1 point) are alternatives, not cumulative items.
• Previous VTE: 3 points if provoked by major surgery, 4 points in all other cases. The two items are never added together.

Indications that apply regardless of the score

Some conditions carry an indication for prophylaxis even when the total remains low. The calculator lists them separately below the result:

• Previous VTE: prophylaxis throughout pregnancy and for 6 weeks after delivery.
• High-risk thrombophilia: antenatal prophylaxis and for 6 weeks, with haematology assessment; antithrombin deficiency and antiphospholipid syndrome have their own regimens.
• Low-risk thrombophilia with a family history of VTE: prophylaxis for 6 weeks in the puerperium.
• BMI ≥ 50 at booking: prophylaxis throughout pregnancy and for 6 weeks after delivery (RCOG 2026 position statement).
• Hyperemesis gravidarum: LMWH within 72 hours, until the risk factor resolves and for a further week.
• Antenatal admission, a stay of ≥ 3 days or readmission in the puerperium: consider prophylaxis.

Clinical references

The RCOG table and thresholds

Weight-banded prophylactic dosing

The 2026 RCOG position statement, aligned with the NHS England Maternal Care Bundle, replaces the fixed dose with a regimen based on body weight. The 2018 Italian form, however, uses different bands, and in two weight windows the two sources give different doses.

The two rows in bold are the windows of divergence: below 50 kg the Italian form halves the dose, and between 91 and 99 kg it increases it earlier. The calculator flags them automatically when the weight has been entered, and the choice must be justified in the medical record.

Doses in the higher bands may be given in two daily injections. The regimen refers to prophylaxis: therapeutic dosing follows its own criteria.

The Italian reading: SIGO / Fondazione Confalonieri Ragonese 2018 form

The SIGO, AOGOI and AGUI recommendations of the Fondazione Confalonieri Ragonese (Il rischio tromboembolico in gravidanza e puerperio, 2014, revised May 2018) adopt the same factors, the same scores and the same three thresholds as the RCOG table. The score therefore does not change, and presenting two scores would be a fiction. The differences between the two sources lie downstream of the score and there are three of them.

1. The weight bands for dosing do not coincide: the Italian form starts at 50 and 90 kg, the RCOG position statement at 100 kg. There are two windows in which the suggested dose differs — see the table above.
2. The duration in the puerperium is made explicit: at least 10 days above the threshold, extended to 6 weeks in the presence of previous VTE, high-risk thrombophilia, low-risk thrombophilia with a family history, or BMI ≥ 50.
3. Contraindications are listed with numeric thresholds — platelets < 75 × 10⁹/L, blood pressure > 200/120 mmHg, placenta praevia, recent stroke, severe liver and renal disease — whereas RCOG leaves them to clinical judgement.

The calculator automatically recognises the dosing divergence when the weight has been entered, derives the duration with its reason, and compares the thresholds of the two sources at every calculation: if they ever diverged, it would flag this without anyone having to remember.

Indications considered not appropriate: SISET–SIGO statement

The joint statement of the Italian Society for the Study of Haemostasis and Thrombosis (SISET) and SIGO marks out the opposite side: heparin prescribed without an indication. The calculator refers to it in three situations:

• Isolated heterozygosity for factor V Leiden or prothrombin G20210A, without previous VTE and without a family history: it scores 1 point, but one point is not an indication.
• Antithrombin deficiency: increased prophylactic dose (enoxaparin 40 mg every 12 hours, dalteparin 5000 IU every 12 hours) and dedicated haematology management, not the standard dose.
• ART and recurrent miscarriage: they count as risk factors, but in the absence of antiphospholipid syndrome they are not an independent indication for heparin.

The statement also rules out universal thrombophilia screening in pregnant women without a personal or family history of VTE.

What changed with the 2026 position statement

• BMI ≥ 50 at booking: LMWH prophylaxis throughout pregnancy and for 6 weeks after delivery.
• Hyperemesis gravidarum requiring admission: LMWH within 72 hours, continued until the risk factor resolves and for a further week.
• Weight-banded dosing instead of a fixed dose.
• The scores of the individual factors and the antenatal and postpartum thresholds are unchanged from the 2015 edition amended in 2023.

Limitations of the model

• The scoring system was built by consensus from odds ratios in the literature, not from a multivariable analysis: the weights are not regression coefficients and the total is not a probability.
• The fourth edition of the guideline is in preparation: until it is published, RCOG advises following the current edition with the amendments of the position statement.
• The 2018 Italian SIGO/Fondazione Confalonieri Ragonese form adopts this same table, so the score is transferable. ACOG and ASH, by contrast, use different selection criteria not based on a cumulative score: the result of this calculator cannot be transferred to those pathways without reservations.
• The Italian form dates from 2018 and does not include the three amendments of the 2026 RCOG position statement (BMI ≥ 50, hyperemesis, weight-banded dosing): where the two documents diverge, the calculator says so rather than choosing.

References

Sources

• Royal College of Obstetricians and Gynaecologists — Reducing the Risk of Venous Thromboembolism during Pregnancy and the Puerperium. Green-top Guideline No. 37a, third edition, April 2015, amended 2023. This is the version from which all the scores and thresholds in this calculator are taken.
• Royal College of Obstetricians and Gynaecologists — Position statement: Green-top Guideline 37a, 2026. Amendments pending the fourth edition, aligned with the NHS England Maternal Care Bundle: BMI ≥ 50, hyperemesis gravidarum, weight-banded dosing.
• Royal College of Obstetricians and Gynaecologists — Thrombosis and Embolism during Pregnancy and the Puerperium: Acute Management. Green-top Guideline No. 37b, for the treatment of the acute event.
• NHS England — The Maternal Care Bundle, with which the 2026 position statement is aligned.
• SIGO, AOGOI, AGUI — Fondazione Confalonieri Ragonese — Il rischio tromboembolico in gravidanza e puerperio, 2014, revised May 2018, with the Algoritmo di valutazione del rischio tromboembolico in ostetricia and the Scheda di valutazione del rischio di tromboembolismo venoso. This is the source of the Italian reading presented alongside on this page.
• SISET and SIGO — Statement condiviso: prevenzione del tromboembolismo venoso associato alla gravidanza. Appropriate and inappropriate indications for heparin in pregnancy.
• Istituto Superiore di Sanità — ItOSS — Il tromboembolismo venoso in gravidanza e in puerperio, December 2021. Italian national dossier on risk assessment, diagnosis and treatment.