Pregnancy · Risk screening

Preeclampsia Risk Calculator

A simple risk-factor check that tells you whether to take low-dose aspirin from 12-16 weeks. Aligned with USPSTF 2021, ACOG, and NICE NG133 — plus the symptoms to call your midwife about today.

Last reviewed 28 May 2026

Preeclampsia risk factors

Should I take low-dose aspirin in pregnancy?

High-risk factors

ONE or more of these → aspirin is recommended.

Moderate-risk factors

TWO or more of these (with no high-risk factors) → consider aspirin.

Tick every risk factor that applies to you to see your recommended pathway.

Should I take aspirin during pregnancy?

The honest answer for most women: only if you have at least one high-risk factor, or at least two moderate ones. Use the checklist in the calculator above. Aspirin isn’t a take-it-just-in-case thing — trials show the benefit is concentrated in the higher-risk groups.

  • One high-risk factor → aspirin recommended.
  • Two or more moderate-risk factors → aspirin recommended.
  • One or no moderate factor only → routine antenatal monitoring is enough.

What is preeclampsia, in plain English?

Preeclampsia is a pregnancy condition where your blood pressure goes up after 20 weeks and protein starts spilling into your urine. The root cause is the placenta — in early pregnancy, the placenta burrows shallow blood vessels into the wall of your womb. When those vessels don’t remodel properly, the placenta becomes oxygen-starved and releases inflammatory signals into your bloodstream from around 16-20 weeks. Your blood vessels react by tightening up — and that’s when your blood pressure rises and your kidneys, liver, brain, and clotting system can start struggling. It happens in roughly 1 in 25 pregnancies.

What are the warning signs I should call my midwife about?

Call your midwife or maternity triage TODAY if you have any of these:

  • Severe headache that paracetamol doesn’t shift.
  • Blurred vision, double vision, flashing lights, or spots in your sight.
  • Pain just under your right ribs (where your liver sits).
  • Sudden swelling of face, hands, or feet — especially if it’s a noticeable overnight change.
  • Vomiting in the third trimester (different from morning sickness).
  • Feeling generally “just not right” — mums’ gut instinct counts here.
  • Home BP cuff reading 140/90 or higher twice, four hours apart.

Call 999 (UK) or maternity emergency triage if you have any of these: BP 160/110 or higher, seizure, very severe headache with confusion, sudden severe shortness of breath, severe right-upper tummy pain with vomiting, or your baby’s movements have changed or reduced.

How does aspirin actually work for preeclampsia?

Low-dose aspirin shifts the balance in your blood vessels away from tightening signals (thromboxane) toward relaxing signals (prostacyclin). That helps the placenta’s shallow blood vessels remodel properly during the second-trimester window when things normally go wrong in preeclampsia. The ASPRE trial (NEJM 2017) showed a roughly 62% relative risk reduction in preterm preeclampsia in women with risk factors. A 2021 USPSTF meta-analysis put the overall reduction at 10-25% with the largest benefit in preterm preeclampsia — the type that matters most because it’s the one that ends pregnancies early.

When should I start aspirin and at what dose?

  • Dose: 75-150 mg once daily (NICE NG133), or 81 mg once daily (USPSTF). 100 mg is also commonly used in trials.
  • Start: Between 12 and 16 weeks of pregnancy. Definitely before 20 weeks.
  • When in the day: Evening with food. Hermida 2010 showed evening dosing had a slightly better effect on overnight BP than morning dosing.
  • Stop: Usually continued to delivery. Your obstetric team will tell you when to stop — typically 7-10 days before a planned caesarean or planned epidural.
  • Don’t use higher doses (325 mg+) — safety data only supports low-dose for pregnancy use.

Practical scenarios — real-world use cases

Scenario 1: First pregnancy, age 32, no other risk factors

One moderate risk factor (first pregnancy). Aspirin is not recommended. Routine antenatal BP / urine checks are enough. Keep an eye on any of the warning signs above.

Scenario 2: First pregnancy, BMI 36, age 41

Three moderate risk factors (first pregnancy, BMI ≥ 35, age ≥ 40). Aspirin is recommended — start 75-150 mg from 12-16 weeks. Get a home BP cuff. Discuss extra growth scans with your team if any other risk emerges.

Scenario 3: Type 1 diabetes from before pregnancy

One high-risk factor. Aspirin is recommended — start at the booking visit or as soon as pregnancy is confirmed, no later than 16 weeks. You’ll have specialist diabetes-pregnancy care anyway; flag the aspirin with that team.

Scenario 4: Previous mild preeclampsia at 38 weeks with first baby

One high-risk factor (previous preeclampsia). Aspirin is recommended — start as soon as pregnancy is confirmed, ideally by 12-16 weeks. Get a home BP cuff for from 20 weeks. Around 16% recurrence rate; aspirin cuts that further.

Scenario 5: Twin pregnancy from IVF, otherwise healthy

One high-risk factor (multiple pregnancy) plus one moderate (IVF). Aspirin is recommended. Twin pregnancies need extra BP / growth monitoring as standard anyway.

How do I check my own blood pressure correctly at home?

  1. Buy an upper-arm cuff that’s validated by the British Hypertension Society or ESH (look on stridebp.org). Don’t use a wrist cuff — they read 5-10 mmHg out.
  2. Empty bladder. Sit quietly for 5 minutes. Don’t talk during.
  3. Back supported, both feet flat on floor, arm supported at heart level (rest on a table).
  4. Cuff on bare upper arm; tubing on the inside of your elbow.
  5. Take two readings 1-2 minutes apart. Use the second one.
  6. Same time of day each time; record both numbers.

Most antenatal services give you a target like “below 135/85”. Call if BP is 140/90+ twice 4 hours apart; emergency if 160/110 or higher.

Lifestyle — what can I do besides aspirin?

  • Calcium — 1 g/day if your dietary intake is low (under 600 mg/day, WHO recommendation; relevant if you avoid dairy).
  • 150 minutes/week moderate exercise — walking, swimming, prenatal yoga.
  • Reduce salt only if you’ve been advised to (mild restriction; don’t go strict).
  • Adequate sleep, stress management, hydration.
  • Treat existing conditions well — chronic hypertension, diabetes, kidney disease, lupus.

NOT shown to help: vitamin C, vitamin E, garlic supplements, fish oil. The 2010 USPSTF and 2014 Cochrane reviews looked at these — no clear benefit.

What is HELLP syndrome and how do I spot it?

HELLP is the severe end of preeclampsia: Haemolysis, Elevated Liver enzymes, Low Platelets. The classic presentation is pain under your right ribs that won’t go away, often with nausea / vomiting and a general “really unwell” feeling. Sometimes BP is only mildly raised — don’t rely on BP alone to rule it out. Treatment is delivery, usually within hours of diagnosis. About 1 in 1000 pregnancies. Any severe right-upper tummy pain in the third trimester needs same-day maternity assessment.

Can preeclampsia happen AFTER birth?

Yes — postpartum preeclampsia happens in up to 0.3% of women who had no hypertension during pregnancy at all, and more often in women who had any pregnancy hypertension. Peak time: 3-7 days after delivery, but it can happen up to 6 weeks postpartum. Symptoms are the same as during pregnancy. Many maternal deaths from preeclampsia happen postpartum because nobody is expecting it. If you had any pregnancy hypertension, keep your home BP cuff for the first 6 weeks; if you didn’t, the warning signs above still apply.

Long-term — what does having had preeclampsia mean?

Your future risk of cardiovascular disease (heart attack, stroke, high BP, type 2 diabetes, chronic kidney disease) is roughly doubled compared to women who never had preeclampsia. ACOG and RCOG both flag this as a major CV risk marker. What to do:

  • Get a postpartum cardiovascular check 6-12 weeks after delivery — BP, weight, fasting glucose, lipid panel.
  • Annual BP check after that.
  • Maintain healthy weight, Mediterranean-style diet, 150 min/week moderate exercise.
  • Don’t smoke.
  • Tell future GPs about your history (it affects their CV risk calculation).

Limitations of this tool

  • This is a screening triage, not a numerical risk percentage. Research-grade models (Fetal Medicine Foundation triple-test, NICE prediction equation) add BP, uterine artery Doppler, and blood markers (PlGF, PAPP-A) for a precise probability.
  • Risk-factor lists differ slightly between USPSTF, ACOG, RCOG, and NICE. We use the broadest USPSTF 2021 list.
  • Aspirin should not be started without medical input if you’re on other anticoagulants, have peptic ulcer disease, or have a bleeding disorder.
  • This calculator does not detect or diagnose preeclampsia once it develops — only your BP, urine and bloods can.
  • Educational only; doesn’t replace your antenatal team.

Sources

  • U.S. Preventive Services Task Force. Aspirin Use to Prevent Preeclampsia and Related Morbidity and Mortality. JAMA 2021;326:1186-91.
  • ACOG. Committee Opinion No. 743: Low-Dose Aspirin Use During Pregnancy. Obstet Gynecol 2018;132:e44-52.
  • NICE. Hypertension in pregnancy: diagnosis and management (NG133). 2019, updated.
  • Rolnik DL, et al. Aspirin versus placebo in pregnancies at high risk for preterm preeclampsia (ASPRE). N Engl J Med 2017;377:613-22.
  • RCOG Green-top Guideline No. 31. The Investigation and Management of the Small-for-Gestational-Age Fetus.
  • Hermida RC, et al. Bedtime aspirin administration improves blood pressure profile in pregnancy. Chronobiol Int 2010.
  • Cochrane Database. Antiplatelet agents for preventing pre-eclampsia and its complications. Duley L, et al.

Frequently asked questions

What is preeclampsia in simple terms?
Preeclampsia is a pregnancy-only condition where your blood pressure suddenly goes up after 20 weeks and proteins start leaking into your urine. It happens because the placenta didn't bed itself into the womb wall as deeply as it should have in the first trimester. About 1 in 25 pregnancies are affected. Untreated, it can damage your kidneys, liver, brain, blood-clotting, and your baby's growth — so doctors take it seriously and screen for it at every appointment from 20 weeks.
What are the early warning signs of preeclampsia?
The big ones to ring your midwife about TODAY: severe headache that paracetamol doesn't shift, blurred vision or flashing lights, pain just under your right rib cage (this is your liver), sudden swelling of face / hands / feet (overnight changes are the worry), being sick a lot in the third trimester (not normal sickness), feeling 'just not right'. Your home BP cuff reading 140/90 or higher TWO TIMES at least four hours apart is also a same-day call.
Should I take aspirin during pregnancy?
Take low-dose aspirin (75-150 mg in UK, 81 mg in US) once daily from 12-16 weeks through to birth IF you have one of these high-risk things: previous preeclampsia, chronic high blood pressure before pregnancy, kidney disease, type 1 or type 2 diabetes from before pregnancy, autoimmune disease (lupus, antiphospholipid syndrome), or you're carrying twins / triplets. Also consider it if you have TWO of: first pregnancy, over 40, BMI 35+, family history of preeclampsia (mum/sister), 10+ year gap since last pregnancy, or pregnancy from IVF / egg donation. The ASPRE trial (NEJM 2017) showed it cuts preterm preeclampsia by around 80% in high-risk women.
Is low-dose aspirin safe in pregnancy?
Yes — tens of thousands of pregnancies have been studied. At 81 mg/day, the rate of major bleeding, placental abruption, or harm to baby is no different from placebo. The key is LOW dose (75-150 mg). Higher doses (325 mg+) are NOT safe in pregnancy. Most obstetric teams will ask you to stop 7-10 days before a planned caesarean or epidural — they'll give you the exact timing.
When should I start taking aspirin?
Between 12 and 16 weeks of pregnancy. Definitely before 20 weeks — after that, the placenta has already finished its critical remodelling, so aspirin has less effect. If you only realise after 16 weeks that you should be taking it, still start — there is some ongoing benefit up to 28 weeks. Take it in the evening with food (slightly more effective on overnight blood pressure, per Hermida 2010).
How often should I check my blood pressure at home?
If you're low-risk: no need to check at home, but pay attention to your routine antenatal BP readings. If you're high-risk OR borderline: a home BP cuff (BHS / ESH validated cuff, NOT a wrist cuff) used 2-3 times a week from 20 weeks onwards. Sit quietly for 5 minutes first, both feet flat, cuff at heart level. Two readings 1-2 minutes apart. Call your midwife if BP is 140/90 or higher TWICE four hours apart. Call 999 / maternity triage if BP is 160/110 or higher.
What does protein in urine mean during pregnancy?
Pregnancy doubles your kidney filtration, and a little protein passing through is normal. Your urine dipstick is checked at every visit. 'Trace' or '1+' once is rarely worrying on its own. '2+' or '3+' or persistent '1+' — your midwife will send a urine sample to the lab for a protein-creatinine ratio (PCR ≥30 mg/mmol or albumin-creatinine ratio ≥8 mg/mmol = significant proteinuria). Significant proteinuria + new high BP = preeclampsia diagnosis.
Can I prevent preeclampsia?
Some risk is hard-wired (your genes, age, twin pregnancy) but several things help. (1) Aspirin if indicated. (2) Calcium 1-2 g/day if your diet is low-calcium (WHO recommendation for low-income settings — RCOG says consider if dietary calcium is below 600 mg/day). (3) Optimise weight before pregnancy — every BMI point above 25 raises risk. (4) Treat existing high BP / diabetes / kidney issues before pregnancy. (5) Take a normal prenatal multivitamin (folate, vit D). NOT proven to help: vitamin C, vitamin E, garlic, fish oil.
What's the difference between high blood pressure in pregnancy and preeclampsia?
Three different things. (1) Chronic hypertension = high BP BEFORE pregnancy or before 20 weeks. (2) Gestational hypertension = new high BP after 20 weeks but NO protein in urine and no other problems — affects 6% of pregnancies; about 25% progress to full preeclampsia. (3) Preeclampsia = new high BP after 20 weeks PLUS either protein in urine OR other organ involvement (kidneys, liver, low platelets, lung fluid, neurological problems, baby growth restriction). All three are taken seriously, but preeclampsia is the most urgent because it can become eclampsia (seizures) or HELLP syndrome.
What is HELLP syndrome?
HELLP stands for Haemolysis (red cells breaking up), Elevated Liver enzymes (your liver inflamed), Low Platelets (clotting cells low). It's the severe end of preeclampsia and a true emergency — it can cause liver bleeding, stroke, or DIC (disseminated intravascular coagulation). Classic symptom: pain under your right ribs that won't go away, sometimes with nausea/vomiting and a general 'really unwell' feeling. Diagnosed on bloods. Treatment is delivery, usually within hours of diagnosis. About 1 in 1000 pregnancies.
Will my baby be okay if I have preeclampsia?
Most babies are fine, especially if preeclampsia is mild and develops near term. The risks rise the earlier in pregnancy preeclampsia starts. Preeclampsia can cause baby's growth to slow (because the placenta isn't working as well), so you'll have extra growth scans and Doppler ultrasound to check blood flow. If preeclampsia is severe, delivery may need to happen earlier than full-term — your team will weigh the risks of prematurity against the risks of staying pregnant. The outcomes from modern UK / US units are excellent for both mum and baby in 95%+ of cases.
How is preeclampsia treated?
There's no medication that cures preeclampsia — only delivery does that. The aim of treatment before delivery is to keep your blood pressure controlled (so it doesn't cause stroke or seizure) and watch carefully for worsening. Common BP medications safe in pregnancy: labetalol, nifedipine, methyldopa. If preeclampsia becomes severe, you may be admitted; if you have severe features close to 37 weeks, delivery is usually offered. Severe preeclampsia with seizures (eclampsia) is treated with IV magnesium sulphate (MgSO4).
Can preeclampsia happen after birth?
Yes — postpartum preeclampsia can develop up to 6 weeks after delivery, even if you had perfect blood pressure during pregnancy. It's commonest in the first week postpartum. Symptoms are the same as pregnancy preeclampsia (severe headache, vision changes, swelling, BP 140/90+). Many maternal deaths from preeclampsia happen postpartum because women (and sometimes clinicians) don't expect it. Worth a home BP cuff for the first 6 weeks if you had any pregnancy hypertension.
I had preeclampsia in my last pregnancy — will I get it again?
Your risk is higher than average — around 16% recurrence rate (vs 3-5% in the general population). The risk depends on how severe it was last time and how early it appeared. Mild near-term preeclampsia last time: low recurrence (~10%). Severe early-onset preeclampsia last time: up to 25-50% recurrence. Aspirin from 12-16 weeks in the next pregnancy is essential — cuts recurrence by 24% per the Cochrane review. Discuss with maternal-fetal medicine before the next pregnancy if you can.
Does preeclampsia mean I'll get high blood pressure later in life?
Your risk of cardiovascular disease — heart attack, stroke, type 2 diabetes, chronic kidney disease — is roughly DOUBLED compared to women who never had preeclampsia. This isn't a curse — it's information. Get a postpartum cardiovascular check 6-12 weeks after birth (BP, weight, fasting glucose, lipids), then annual check-ups. Mediterranean-style eating, 150 min/week of moderate exercise, not smoking, healthy weight — the same lifestyle that reduces risk in everyone, but more important for you. The ACOG and RCOG both flag preeclampsia as a strong CV risk marker.
Are there blood tests that predict preeclampsia?
Yes, but they're used selectively. The PlGF (placental growth factor) blood test, often combined with sFlt-1 (sFlt-1:PlGF ratio), has good evidence for PREDICTING short-term preeclampsia risk and is now NHS-funded for women with suspected preeclampsia between 20-34 weeks. A low PlGF or high sFlt-1:PlGF ratio means worry; a normal ratio strongly reassures (negative predictive value over 95% for 1-week preeclampsia onset). Not used universally yet; ask your team if available.
Does this calculator replace the FMF / NICE triple-test prediction?
No — it's a simpler triage. The Fetal Medicine Foundation's first-trimester combined screen uses your blood pressure, uterine artery Doppler, PlGF, PAPP-A and your risk factors to give a numerical probability. NICE recommends using the binary risk-factor approach used here for who should take aspirin; the FMF model is more precise but needs a specialist 12-week scan. Both end up with the same aspirin recommendation in most high-risk women.
How does this relate to other calculators on BumpBites?
Companion: /calculators/gdm-risk for the diabetes side (overlapping risk factors); /calculators/pregnancy-bmi for weight-driven risk; /calculators/aspirin-pe-prevention for the clinician-facing dosing tool; /calculators/preeclampsia-diagnosis if you're already symptomatic; /calculators/hellp-classifier for the severe-end picture; /calculators/postpartum-mood-warning for the postpartum recovery period.

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