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What is Pre-eclampsia Risk Calculator?
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Pre-eclampsia is a multi-organ disorder of pregnancy characterised by new-onset hypertension (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on two occasions at least 4 hours apart) at or after 20 weeks of gestation, with one or more features of organ dysfunction including proteinuria, renal impairment, thrombocytopaenia, liver dysfunction, pulmonary oedema, or uteroplacental dysfunction. It affects approximately 3-5% of pregnancies globally and is a leading cause of maternal and perinatal mortality. The Fetal Medicine Foundation (FMF) first-trimester screening algorithm combines maternal risk factors with three objective biomarkers — mean arterial pressure (MAP), uterine artery pulsatility index (UtA PI) measured by Doppler ultrasound, and placental growth factor (PlGF) in serum — to calculate an individualised risk of developing pre-eclampsia before 37 weeks (preterm PE) and before 34 weeks (early PE). A risk of 1:100 or greater for preterm pre-eclampsia at the 11-13+6 week combined screening visit identifies women who benefit from prophylactic low-dose aspirin (150 mg nightly from 11-14 weeks), which reduces preterm PE risk by approximately 62% in the high-risk group. PAPP-A (pregnancy-associated plasma protein-A) is an additional biochemical marker used in some algorithms. In established suspected pre-eclampsia, the sFlt-1/PlGF ratio is used to confirm or exclude the diagnosis and predict severity: a ratio below 38 has a high negative predictive value (rule-out); a ratio above 85 confirms significant disease.
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सूत्र
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FMF PE Risk = Combined algorithm: Maternal factors + MAP (mmHg) + UtA PI (Doppler) + PlGF (MoM) + PAPP-A (MoM); High risk ≥1:100 for preterm PE → aspirin 150mg nightly from 11-14 weeks; sFlt-1/PlGF ratio: <38=rule out, 38-85=intermediate, >85=confirm PEVariable Legend
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| प्रतीक | नाव | एकक | वर्णन |
|---|---|---|---|
| MAP | Mean Arterial Pressure | mmHg | Diastolic BP + (SBP-DBP)/3; measured bilaterally; higher arm used; key biomarker for PE risk |
| UtA PI | Uterine Artery Pulsatility Index | dimensionless | Doppler marker of uterine artery resistance; elevated PI indicates impaired trophoblast invasion |
| PlGF | Placental Growth Factor | MoM | Angiogenic placental biomarker; reduced early in pre-eclampsia; expressed as multiple of median |
| sFlt-1 | Soluble FMS-like Tyrosine Kinase-1 | pg/mL | Anti-angiogenic factor elevated in established PE; used with PlGF as diagnostic ratio |
How to Pre-eclampsia Risk Calculator
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- 1At the 11-13+6 week combined screening visit, collect maternal risk factors: age, BMI, ethnicity, smoking status, parity, conception method, family history of PE, personal history of PE, chronic hypertension, diabetes, SLE or antiphospholipid syndrome, and inter-pregnancy interval.
- 2Measure mean arterial pressure (MAP) bilaterally in both arms using a standardised protocol: MAP = diastolic BP + (systolic BP − diastolic BP)/3. Use the higher of the two arm measurements.
- 3Perform uterine artery Doppler at 11-13+6 weeks: measure the uterine artery pulsatility index (UtA PI) bilaterally by transvaginal or transabdominal Doppler. Impaired trophoblast invasion is reflected by elevated UtA PI (normal UtA PI <1.5).
- 4Measure serum PlGF (placental growth factor) — a placenta-derived angiogenic protein that is reduced in women who will develop pre-eclampsia. PlGF is converted to a multiple of the median (MoM) corrected for gestational age, weight, and ethnicity.
- 5Optional: measure PAPP-A, which is also reduced in pre-eclampsia. PAPP-A MoM is incorporated in extended algorithms.
- 6Enter all parameters into a validated Bayes theorem-based FMF algorithm (available via the FMF calculator or licensed software) to generate an individual risk for preterm PE (<37 weeks) and early PE (<34 weeks). A risk of ≥1:100 for preterm PE is the treatment threshold.
- 7Prescribe aspirin 150 mg orally at night from 11-14 weeks to all women at high risk (≥1:100 for preterm PE). Continue until 36 weeks gestation. Monitor blood pressure and urine protein at every antenatal visit.
Worked Examples
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No aspirin indicated; routine antenatal monitoring
Normal MAP, normal UtA PI, and adequate PlGF combine with a low-risk obstetric history to produce reassuringly low preterm PE risk. Standard antenatal monitoring is sufficient.
Aspirin 150mg nightly from 12 weeks; enhanced BP and urine monitoring from 20 weeks; USS growth surveillance
Multiple high-risk features (nulliparity, obesity, African ethnicity, elevated MAP, high UtA PI, low PlGF) produce a very high preterm PE risk. Early aspirin reduces this risk by ~62%.
High negative predictive value; outpatient management may be appropriate; recheck in 1 week
An sFlt-1/PlGF ratio below 38 has >99% negative predictive value for ruling out pre-eclampsia requiring delivery within 1 week, supporting safe continued outpatient management with close follow-up.
Admit; magnesium sulfate for seizure prophylaxis; consider delivery; liaise with neonatology
A ratio above 85 (or above 110 before 34 weeks in some guidelines) confirms significant pre-eclampsia and predicts high risk of adverse outcomes. Immediate assessment and likely delivery is indicated.
Real-World Applications
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First-trimester combined PE screening at 11-13+6 weeks to identify women who benefit from prophylactic aspirin 150 mg., representing an important application area for the Preeclampsia Risk in professional and analytical contexts where accurate preeclampsia risk calculations directly support informed decision-making, strategic planning, and performance optimization
Confirming or ruling out pre-eclampsia in women presenting with hypertension or suspected PE symptoms using the sFlt-1/PlGF ratio., representing an important application area for the Preeclampsia Risk in professional and analytical contexts where accurate preeclampsia risk calculations directly support informed decision-making, strategic planning, and performance optimization
Guiding outpatient versus inpatient management decisions in women with borderline PE using the negative predictive value of sFlt-1/PlGF ratio <38., representing an important application area for the Preeclampsia Risk in professional and analytical contexts where accurate preeclampsia risk calculations directly support informed decision-making, strategic planning, and performance optimization
Academic researchers and university faculty use the Preeclampsia Risk for empirical studies, thesis research, and peer-reviewed publications requiring rigorous quantitative preeclampsia risk analysis across controlled experimental conditions and comparative studies
Health economics: targeted aspirin prescribing to high-risk women identified by biomarker screening is cost-effective compared to universal or risk factor-only based prescribing., representing an important application area for the Preeclampsia Risk in professional and analytical contexts where accurate preeclampsia risk calculations directly support informed decision-making, strategic planning, and performance optimization
Special Cases
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Chronic Hypertension
{'title': 'Chronic Hypertension', 'body': 'Women with chronic hypertension are at significantly elevated risk of superimposed pre-eclampsia (incidence approximately 25%). They should receive aspirin from 12 weeks regardless of first-trimester screening result. Differentiating superimposed PE from worsening chronic hypertension can be challenging; the sFlt-1/PlGF ratio is particularly useful in this context.'}
Antiphospholipid Syndrome
In the Preeclampsia Risk, this scenario requires additional caution when interpreting preeclampsia risk results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when preeclampsia risk calculations fall into non-standard territory.
Twin Pregnancy
{'title': 'Twin Pregnancy', 'body': 'Multiple pregnancy independently increases PE risk, particularly in monochorionic twins with twin-to-twin transfusion syndrome. First-trimester screening algorithms for twins differ from singleton algorithms. PlGF MoM values are lower in twin pregnancies, and different thresholds apply. Many guidelines recommend aspirin for all twin pregnancies regardless of screening result.'}
IVF Pregnancy
{'title': 'IVF Pregnancy', 'body': 'IVF pregnancies have elevated PE risk, particularly those conceived with donated oocytes (egg donation), where immunological mismatch between donor genetics and maternal tolerance is thought to increase susceptibility. Aspirin is generally recommended from 12 weeks for all egg donation pregnancies. PAPP-A may be artifactually elevated in IVF pregnancies, reducing its discriminatory value.'}
sFlt-1/PlGF Ratio Interpretation
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| Ratio | Interpretation | Clinical Action |
|---|---|---|
| <38 | Rules out PE (high NPV for 1 week) | Outpatient management; recheck in 1 week |
| 38-85 | Intermediate — monitor closely | Admit or intensify monitoring; twice-weekly recheck |
| >85 (>34 weeks) | Confirms significant PE | Admit; consider delivery; magnesium sulfate |
| >110 (<34 weeks) | Confirms significant PE (preterm threshold) | Specialist management; corticosteroids; delivery planning |
Frequently Asked Questions
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What are the risk factors for preeclampsia?
High-risk factors (any one significantly increases risk): previous preeclampsia (recurrence rate 15-20%), chronic hypertension, type 1 or 2 diabetes, kidney disease, autoimmune disorders (lupus, antiphospholipid syndrome), and multifetal pregnancy (twins/triplets). Moderate-risk factors (two or more combined increase risk): first pregnancy (nulliparity), age over 35 (especially over 40), BMI over 30, family history of preeclampsia (mother or sister), more than 10 years since last pregnancy, and IVF conception. Preeclampsia affects 5-8% of pregnancies worldwide. It develops after 20 weeks gestation (most commonly in the third trimester or immediately postpartum) and is defined by new-onset hypertension (≥140/90 mmHg) plus proteinuria or other organ dysfunction. Early-onset (<34 weeks) preeclampsia is more severe and associated with worse outcomes than late-onset.
Can preeclampsia be prevented?
Low-dose aspirin (81-162 mg daily starting at 12-16 weeks) reduces preeclampsia risk by 15-25% in high-risk women. ACOG recommends it for anyone with one high-risk factor or two or more moderate-risk factors. Calcium supplementation (1,500-2,000 mg/day) may reduce risk in women with low dietary calcium intake, particularly in developing countries. Regular prenatal care: early and frequent blood pressure monitoring enables early detection. Monitoring for warning signs: severe headache that doesn't respond to acetaminophen, vision changes (blurring, seeing spots, light sensitivity), upper abdominal pain (especially right side — liver involvement), sudden swelling of face and hands, and rapid weight gain (>2 lbs/week in third trimester). No proven prevention: adequate rest, reduced salt intake, and exercise haven't been definitively shown to prevent preeclampsia, though they're generally good for pregnancy health. If diagnosed, delivery is the only cure — timing depends on severity and gestational age.
How is preeclampsia diagnosed?
Diagnosis involves new-onset hypertension (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on two occasions at least 4 hours apart) occurring at or after 20 weeks of gestation. This must be accompanied by one or more features of organ dysfunction, such as proteinuria (e.g., ≥0.3 grams in a 24-hour urine collection), renal impairment (creatinine >1.1 mg/dL), or liver dysfunction (elevated transaminases). Other indicators include thrombocytopenia (platelet count <100,000/µL) or pulmonary edema.
How common is preeclampsia, and when does it typically occur?
Preeclampsia affects approximately 2-8% of pregnancies worldwide, making it a significant cause of maternal and perinatal morbidity. While it can develop anytime after 20 weeks of gestation, it most commonly manifests in the third trimester. Early-onset preeclampsia, occurring before 34 weeks, is often more severe and associated with higher risks.
What are the potential complications of preeclampsia for the mother and baby?
For the mother, preeclampsia can lead to serious complications such as eclampsia (seizures), HELLP syndrome (hemolysis, elevated liver enzymes, low platelet count), stroke, acute kidney injury, and pulmonary edema. Fetal complications include intrauterine growth restriction (IUGR), preterm birth due to medically indicated delivery, placental abruption, and stillbirth, often stemming from compromised placental blood flow. Long-term maternal risks include an increased likelihood of developing cardiovascular disease later in life.
Common Mistakes to Avoid
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- !Prescribing aspirin 75 mg instead of 150 mg — the ASPRE trial used 150 mg nightly and this dose is significantly more effective for preterm PE prevention than lower doses.
- !Starting aspirin after 16 weeks — aspirin must be started before 16 weeks (ideally 11-14 weeks) to achieve maximum benefit on trophoblast invasion and placentation.
- !Interpreting a low PlGF result as normal because the absolute value appears reasonable without converting to MoM corrected for gestational age and body weight.
- !Stopping blood pressure and proteinuria monitoring once aspirin has been prescribed — aspirin reduces but does not eliminate PE risk; ongoing monitoring is mandatory.
- !Not measuring blood pressure in both arms — unilateral measurement misses the 10-15% of women with significant inter-arm differences relevant to MAP calculation.
- !Applying singleton screening algorithm thresholds to twin pregnancies — separate twin-specific algorithms and thresholds must be used.
Pro Tip
In first-trimester PE screening, PlGF and UtA PI are the most powerful discriminators for preterm PE. A PlGF MoM below 0.4 combined with elevated UtA PI above 2.0 should heighten clinical suspicion even if the algorithm-generated risk falls just below the 1:100 threshold — consider prescribing aspirin based on clinical gestalt in borderline cases.
Did you know?
The link between aspirin and pre-eclampsia was first suggested in 1985 by John Crandon and colleagues, who observed that women regularly taking low-dose aspirin for other medical conditions appeared to have lower rates of hypertensive complications. The subsequent decades of randomised trials, culminating in the ASPRE trial, confirmed that early high-dose aspirin reduces preterm PE by over 60% in high-risk women — making first-trimester risk stratification one of the most impactful preventive interventions in modern obstetrics.
References
- ›Rolnik DL et al. Aspirin versus Placebo in Pregnancies at High Risk for Preterm Preeclampsia (ASPRE). NEJM 2017.
- ›Zeisler H et al. Predictive Value of the sFlt-1:PlGF Ratio in Women with Suspected Preeclampsia. NEJM 2016.
- ›NICE Guideline NG133 — Hypertension in pregnancy: diagnosis and management. 2019 (updated 2023).
- ›O'Gorman N et al. Competing risks model in screening for preeclampsia by maternal factors and biomarkers at 11-13 weeks' gestation. Am J Obstet Gynecol 2016.
- ›ISSHP Classification, Diagnosis, and Management of Hypertensive Disorders of Pregnancy. Pregnancy Hypertens 2018.
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