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Pre-eclampsia Risk Calculator

Enter maternal age, BMI and risk factors to estimate relative pre-eclampsia risk.

How it is calculated

The tool adds points for each risk factor present. Age: 35 to 39 gives 1 point, 40 or over gives 2. BMI: 25 to under 30 gives 1, 30 to under 35 gives 2, 35 or over gives 3. Yes/no factors: first pregnancy 1, chronic hypertension 4, diabetes 2, previous pre-eclampsia 4, multiple pregnancy 2, family history 1. Then relative risk = 1.18points, shown as a multiplier (0 points gives 1.00×).

This is a teaching model, not a validated screening algorithm. The 18 % per point is an illustrative figure, the points are simple thresholds and nothing is measured (no blood pressure, Doppler or blood tests). A yes/no factor counts only when it is passed as 1. The multiplier compares you with a baseline person of 0 points, it is not a percentage chance. Age and BMI must be above zero. It does not diagnose anything; risk assessment belongs with an obstetrician.

Worked example

A woman aged 37 with a BMI of 31, expecting her first child and with a family history. Age 37 falls in 35 to 39: 1 point. BMI 31 falls in 30 to 34.9: 2 points. First pregnancy: 1 point. Family history: 1 point. Total: 1 + 2 + 1 + 1 = 5 pts. Relative risk: 1.18 to the power 5 = 2.29, shown as 2.29×. In this simplified scale that means about 2.3 times the baseline of a person with 0 points, not a 229 % chance.

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Common mistakes

  • Reading the multiplier as the probability of getting pre-eclampsia. 2.29× is a ratio against the 0-point baseline, not a percentage chance.
  • Treating a low score as reassurance. Many things that matter in real screening, such as blood pressure readings, are not inputs here, so 0 pts says little about an individual pregnancy.
  • Entering the BMI of the current pregnancy weight rather than the BMI before pregnancy. The tool is meant for the pre-pregnancy figure, and a later weight will push the score up.
  • Expecting every ticked or yes-style answer to count. A yes/no factor is only scored when it is submitted as 1; other text like yes is treated as no.
  • Using the result to decide on aspirin or other treatment. This is an educational calculator with illustrative weights, and treatment decisions are made by a clinician using proper screening.

Sources

About this calculator

This pre-eclampsia risk calculator is a simplified educational screening score that combines established maternal risk factors — advanced maternal age, high pre-pregnancy BMI, chronic hypertension, pre-existing diabetes, a first pregnancy (nulliparity), multiple gestation (twins or more), and a personal or family history of pre-eclampsia — into a single relative risk estimate, reflecting the same categories of factors clinicians weigh in first-trimester screening.

Pre-eclampsia (new-onset high blood pressure with organ involvement after 20 weeks) is a leading cause of maternal and fetal complications, which is why real clinical risk assessment combines these factors with blood pressure measurement, uterine artery Doppler, and biomarkers like PlGF under protocols such as the Fetal Medicine Foundation algorithm. This tool is for education only and is not a diagnosis — always discuss actual risk assessment and low-dose aspirin prophylaxis with an obstetrician. The point weights and the 1.18 multiplier per point are illustrative, not taken from a guideline. Guidance such as NICE NG133 and the US Preventive Services Task Force (2021) instead sorts these factors into high- and moderate-risk groups, and one high-risk factor, or more than one moderate-risk factor, is the usual trigger for discussing low-dose aspirin.

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Comments (1)

  • Editorial team

    A single high-risk factor can look unimpressive on this scale. Previous pre-eclampsia or chronic hypertension adds 4 points here, a multiplier of only 1.94, yet guidelines such as NICE and the USPSTF treat one high-risk factor as reason enough to discuss low-dose aspirin. So a modest multiplier is no reassurance. The weights are illustrative, so bring your own history to an obstetrician. Which part of the score would you like explained further?

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