Preeclampsia Risk Calculator — FMF/ACOG First-Trimester Screening

How to Use This Calculator

1. Enter maternal age, BMI, and parity status.
2. Select chronic conditions (HTN, diabetes, ART).
3. Risk category and aspirin indication appear instantly.
4. Use the FMF Algorithm tab to incorporate biomarker MoM values.
5. Use the ACOG tab for US guideline-based factor assessment.

Formula

Example

Frequently Asked Questions

• How is preeclampsia risk assessed in early pregnancy? ▼
  First-trimester preeclampsia screening combines maternal risk factors, biophysical measurements, and biochemical biomarkers to estimate the probability of developing preeclampsia — particularly the more dangerous preterm form before 37 weeks. The Fetal Medicine Foundation (FMF) algorithm, validated in the ASPRE trial, integrates maternal characteristics (age, weight, height, parity, ethnicity, conception method, smoking, chronic conditions), uterine artery pulsatility index (UtA-PI) measured by Doppler ultrasound at 11–13 weeks, mean arterial pressure (MAP), placental growth factor (PlGF), and pregnancy-associated plasma protein-A (PAPP-A). This combined first-trimester screen detects approximately 75–90% of preterm preeclampsia cases at a 10% false-positive rate, far surpassing the detection rate of risk-factor-alone assessment (~40%). Biomarkers are particularly informative: low PlGF (below 0.5 MoM) reflects impaired placentation even before symptoms appear, while elevated UtA-PI indicates increased uterine vascular resistance. ACOG Practice Bulletin 222 recommends a simpler risk-factor-based approach for US practice, classifying patients as high risk (one major factor) or moderate risk (multiple minor factors), with aspirin offered accordingly.
• Who should take low-dose aspirin to prevent preeclampsia? ▼
  According to USPSTF 2021 and ACOG Practice Bulletin 222, low-dose aspirin (81 mg/day in the US; 150 mg/night in the UK/FMF protocol) is recommended for women at high risk of preeclampsia, starting between 12 and 16 weeks of gestation. High-risk indications for aspirin include: prior history of preeclampsia (especially preterm preeclampsia); multifetal gestation; chronic hypertension; type 1 or type 2 diabetes; renal disease; and autoimmune conditions such as systemic lupus erythematosus or antiphospholipid syndrome. Aspirin is also recommended when a woman has two or more moderate-risk factors, including nulliparity, obesity (BMI ≥30 kg/m²), maternal age ≥35 years, low socioeconomic status, African-American race, family history of preeclampsia, prior low birth weight or small-for-gestational-age infant, or conception via assisted reproductive technology (ART). The absolute benefit is greatest in high-risk women, with one large meta-analysis showing a 24% reduction in preeclampsia and a 20% reduction in preterm birth with aspirin started before 16 weeks.
• What is the ASPRE trial and what did it find? ▼
  The ASPRE (Aspirin for Evidence-Based Preeclampsia Prevention) trial, published by Rolnik et al. in the New England Journal of Medicine in 2017, was a randomised, double-blind, placebo-controlled trial conducted at 13 maternity units across six countries. It enrolled 1,776 women identified as high risk for preterm preeclampsia using the FMF combined first-trimester screening algorithm. Participants were randomised to aspirin 150 mg at night or placebo from 11 to 14 weeks until 36 weeks of gestation. The primary outcome — preterm preeclampsia before 37 weeks — occurred in 1.6% of the aspirin group versus 4.3% in the placebo group, representing a 62% relative risk reduction (RR 0.38, 95% CI 0.20–0.74). The absolute risk reduction was 2.7%, giving a number needed to treat (NNT) of approximately 37 to prevent one case of preterm preeclampsia. Aspirin did not significantly reduce term preeclampsia. The trial demonstrated that FMF-based screening combined with 150 mg aspirin at night (higher dose and specific timing than US practice) achieves substantially better prevention than ad hoc risk-factor assessment alone. Subsequent meta-analyses confirmed benefit across multiple aspirin doses when started before 16 weeks.
• What are the major risk factors for preeclampsia? ▼
  Preeclampsia affects 2–8% of pregnancies worldwide and is a leading cause of maternal and perinatal morbidity. Major (high-risk) factors that independently confer substantial risk include: previous preeclampsia (recurrence risk 13–25%, higher if preterm); chronic hypertension (18–25% risk); pre-existing diabetes mellitus type 1 or 2 (10–18% risk); multifetal gestation (14–20% risk); renal disease; and antiphospholipid syndrome. Moderate risk factors that collectively increase risk when two or more are present include: nulliparity, obesity (BMI ≥30), age ≥35 years, Black or African-American ethnicity (higher incidence and severity), family history of preeclampsia in first-degree relative, prior adverse pregnancy outcomes (IUGR, stillbirth), and conception via IVF. The pathophysiology involves abnormal trophoblast invasion of spiral arteries in early placentation, leading to placental ischaemia, release of antiangiogenic factors (sFlt-1, endoglin), and widespread endothelial dysfunction manifesting as hypertension, proteinuria, and multi-organ involvement. Understanding modifiable versus non-modifiable risk factors guides targeted prevention and surveillance planning.
• How is preeclampsia diagnosed? ▼
  Preeclampsia is defined as new-onset hypertension (systolic BP ≥140 mmHg or diastolic ≥90 mmHg on two occasions ≥4 hours apart) after 20 weeks of gestation, in combination with at least one of: proteinuria (≥300 mg/24h, protein:creatinine ratio ≥0.3, or dipstick 2+); thrombocytopenia (platelet count <100,000/μL); renal insufficiency (creatinine >1.1 mg/dL or doubling of baseline without other cause); impaired liver function (elevated transaminases to twice normal); pulmonary oedema; new-onset headache unresponsive to analgesia; or visual disturbances. Notably, proteinuria is no longer required for diagnosis if other end-organ manifestations are present — this revision was adopted by ACOG in 2013. Severe features include systolic ≥160 or diastolic ≥110, severe headache, visual scotomata, RUQ pain, platelet count <100,000, creatinine >1.1, or pulmonary oedema. The key diagnostic distinction is from gestational hypertension (elevated BP without end-organ involvement) and chronic hypertension. Superimposed preeclampsia on chronic hypertension is identified by new proteinuria, sudden worsening of BP control, or new end-organ features. HELLP syndrome (haemolysis, elevated liver enzymes, low platelets) is a severe variant.

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