Pre-Eclampsia

Epidemiology and Risk Factors

Pre-eclampsia affects up to 5% of first pregnancies and around 1-2% of subsequent pregnancies. Severe pre-eclampsia is less common but accounts for most of the morbidity. The MBRRACE-UK confidential enquiries have reported a recent rise in maternal deaths from pre-eclampsia and eclampsia, with most considered preventable.

Risk factors are commonly grouped into high-risk and moderate-risk categories. Clinicians offer aspirin prophylaxis to any woman with one high-risk factor or two or more moderate-risk factors.

Advise eligible women to take aspirin 150 mg daily from 12 weeks until birth. The ASPRE trial supports this dose, having demonstrated a 62% reduction in preterm pre-eclampsia. Furthermore, 150 mg is the dose used in most current UK protocols.

Pathophysiology

The exact cause of pre-eclampsia remains unknown. However, most authorities consider it a placental disease driven by abnormal trophoblastic invasion of the maternal spiral arteries.

In a normal pregnancy, the trophoblast invades the spiral arteries of the uterus, destroying their muscular walls and creating a high-flow, low-resistance circulation that supports the growing placenta. In pre-eclampsia, by contrast, this remodelling is incomplete, leaving a high-resistance, low-flow uteroplacental circulation.

As a result, placental hypoperfusion produces oxidative stress and releases anti-angiogenic factors, notably soluble fms-like tyrosine kinase-1 (sFlt-1), while reducing placental growth factor (PlGF). This imbalance drives widespread maternal endothelial dysfunction, increased vascular permeability, and the multisystem features that define the disease.

Clinical Features

Pre-eclampsia is diagnosed when there is new hypertension after 20 weeks of gestation (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on two occasions at least four hours apart) accompanied by one or more of:

• Significant proteinuria, defined as urinary protein:creatinine ratio (PCR) ≥30 mg/mmol or albumin:creatinine ratio (ACR) ≥8 mg/mmol.
• Maternal organ dysfunction: renal impairment, hepatic involvement, neurological complications, or haematological involvement (e.g. thrombocytopenia).
• Uteroplacental dysfunction: fetal growth restriction or abnormal umbilical artery Doppler findings.

Many women remain asymptomatic in early disease, which is why routine antenatal monitoring of blood pressure and urine matters. However, when symptoms occur, they typically include:

• Frontal headache.
• Visual disturbance (blurred vision, flashing lights).
• Right upper quadrant or epigastric pain (from hepatic capsular distension).
• Sudden non-dependent oedema of the face, hands or feet.
• Hyperreflexia.
• Reduced fetal movements.

Severe pre-eclampsia means sustained blood pressure ≥160/110 mmHg, significant maternal symptoms, or biochemical evidence of severe organ dysfunction (such as platelets <100 x 10⁹/L, deranged liver enzymes, or rising creatinine). Consequently, it carries a high short-term risk of complications and warrants urgent senior obstetric input.

Investigations and Screening

Initial assessment of suspected pre-eclampsia includes:

• Blood pressure, measured manually with an appropriate cuff size; ambulatory or home monitoring may complement clinic readings.
• Urinalysis with dipstick screening at every antenatal contact; if 1+ or more, quantify with PCR or ACR rather than 24-hour urine collection.
• Blood tests: full blood count, urea and electrolytes, urate, liver function tests. Look for thrombocytopenia, rising urate, deranged transaminases, or impaired renal function.
• Fetal assessment: ultrasound for fetal growth, amniotic fluid volume, and umbilical artery Doppler.

PlGF-Based Testing

Placental growth factor (PlGF)-based testing helps rule in or rule out pre-eclampsia in women with suspected disease between 20 weeks and 36+6 weeks of gestation. A low PlGF (or high sFlt-1/PlGF ratio) supports the diagnosis and increases the likelihood of delivery within 14 days. A normal result has a high negative predictive value and supports outpatient management.

Studies show that PlGF testing shortens time to diagnosis and reduces serious maternal morbidity. As a result, it now represents standard of care in most UK units. In particular, it has value for groups at higher risk of severe adverse outcomes, including women from Black, Asian and minority ethnic backgrounds.

Management

The aims of management are to control maternal blood pressure, prevent eclampsia, monitor maternal and fetal wellbeing, and time delivery to balance the risks of prematurity against those of continuing pregnancy. Critically, delivery of the placenta remains the only definitive cure.

Blood Pressure Control

Start antihypertensive treatment when blood pressure is sustained at ≥140/90 mmHg, aiming for a target of 135/85 mmHg or less. The agents used in UK practice are:

For acute severe hypertension (≥160/110 mmHg), use intravenous labetalol, oral nifedipine, or intravenous hydralazine. Importantly, ACE inhibitors, angiotensin receptor blockers, and thiazide diuretics are contraindicated in pregnancy because of fetal renal and developmental risks.

Magnesium Sulphate

Give intravenous magnesium sulphate to women with severe pre-eclampsia, to prevent and treat eclamptic seizures. Also give it when birth is planned within 24 hours.

The standard UK regimen is a 4 g intravenous loading dose over 5 to 15 minutes, followed by a maintenance infusion of 1 g per hour. Continue the infusion for 24 hours after birth or after the last seizure, whichever is later. Throughout, monitor reflexes, respiratory rate, and urine output for signs of magnesium toxicity.

Corticosteroids and Timing of Birth

If preterm birth is anticipated, offer antenatal corticosteroids to promote fetal lung maturity, alongside magnesium sulphate for neuroprotection where indicated. Furthermore, these two interventions are routinely given together when planned early birth is required for pre-eclampsia.

Individualise the timing of birth. Women with pre-eclampsia at term are usually offered planned birth from 37 weeks. Consider preterm delivery when there is severe or deteriorating disease, fetal compromise, or maternal complications such as HELLP syndrome. Make these decisions at consultant obstetric level with neonatal involvement.

Complications

Pre-eclampsia is a multisystem disorder with potentially serious maternal and fetal complications. Earlier onset typically leads to worse outcomes.

Maternal complications include:

• Eclampsia – tonic-clonic seizures; an obstetric emergency.
• HELLP syndrome – haemolysis, elevated liver enzymes, low platelets.
• Acute kidney injury.
• Disseminated intravascular coagulation.
• Pulmonary oedema and acute respiratory distress.
• Cerebrovascular haemorrhage.
• Maternal death.

Fetal complications include placental abruption, fetal growth restriction, iatrogenic and spontaneous prematurity, and stillbirth.

Postnatal Care

Pre-eclampsia resolves following delivery of the placenta. However, women remain at risk of complications, including eclampsia, in the first few postnatal days. Therefore, UK practice is inpatient monitoring of blood pressure for at least 72 hours, with most cases stabilising by day five.

Many women continue antihypertensive therapy postnatally. Titrate doses down as blood pressure improves, aiming to maintain 135/85 mmHg or less. Importantly, stop methyldopa within two days of birth because of its association with postnatal depression.

Follow-up

All women who have had pre-eclampsia need a 6 to 8 week postnatal medical review. This should cover blood pressure, ongoing medication, planning for future pregnancies, and counselling about long-term cardiovascular risk. In addition, advise women that the risk of pre-eclampsia rises in subsequent pregnancies, and that early booking with consideration of aspirin prophylaxis matters.

A history of pre-eclampsia approximately doubles a woman’s lifetime risk of cardiovascular disease, including coronary artery disease, heart failure and stroke. Therefore, encourage women to attend their GP for periodic review of blood pressure, weight, lipids, and glucose, and offer lifestyle advice on diet, exercise and smoking cessation.

Equity, Safety and Professionalism

Outcomes from pre-eclampsia differ markedly across populations. MBRRACE-UK reports consistently show that women from Black ethnic backgrounds are more than twice as likely to die from pregnancy-related causes as White women, with women from Asian backgrounds also at increased risk. Socioeconomic deprivation acts as an independent risk factor. Furthermore, a high proportion of maternal deaths from pre-eclampsia involve elements of care that could have been improved, with delayed recognition, inadequate monitoring, and missed escalation recurring as themes.

Shared decision-making sits central to management. Women face difficult choices about timing of birth, mode of delivery, and continuation of antihypertensive therapy in subsequent pregnancies. Therefore, clear written information, an interpreter where needed, and the use of standardised early warning systems (MEOWS or equivalent) support safer care.

Recent Changes and Controversies

The diagnostic definition of pre-eclampsia has broadened in recent years. Specifically, pre-eclampsia can now be diagnosed without proteinuria if maternal organ dysfunction is present. This reflects the multisystem nature of the disease.

PlGF-based testing now sits embedded in NHS practice (NICE DG49, 2022). Notably, the MBRRACE-UK 2024 report highlighted that none of the women who died from pre-eclampsia in the audit period had received a PlGF test, and called for universal access to the test across UK trusts.

The aspirin dose for prophylaxis remains an area of evolving practice. UK guidance specifies a range of 75 to 150 mg. However, the ASPRE trial demonstrated substantially greater benefit at 150 mg, and most current UK protocols now specify the higher dose.

Finally, spot urinary PCR or ACR has largely replaced 24-hour urine collection for quantifying proteinuria, being quicker and equally accurate for the diagnostic threshold.

References

1. National Institute for Health and Care Excellence. Hypertension in pregnancy: diagnosis and management. NICE guideline NG133. London: NICE; 2019 (amended 2023). Available from: https://www.nice.org.uk/guidance/ng133 [Accessed May 2026].

2. National Institute for Health and Care Excellence. PLGF-based testing to help diagnose suspected preterm pre-eclampsia. Diagnostics guidance DG49. London: NICE; 2022. Available from: https://www.nice.org.uk/guidance/dg49 [Accessed May 2026].

3. Rolnik DL, Wright D, Poon LC, et al. Aspirin versus Placebo in Pregnancies at High Risk for Preterm Preeclampsia (ASPRE trial). N Engl J Med. 2017;377:613-622.

4. Knight M, Bunch K, Felker A, et al, on behalf of MBRRACE-UK. Saving Lives, Improving Mothers’ Care: Lessons learned to inform maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2020-22. National Perinatal Epidemiology Unit, University of Oxford; 2024.

5. National Institute for Health and Care Excellence. Preterm labour and birth. NICE guideline NG25. London: NICE; 2015 [updated 2022]. Available from: https://www.nice.org.uk/guidance/ng25 [Accessed May 2026].

6. National Institute for Health and Care Excellence. Hypertension in pregnancy. Quality standard QS35. London: NICE; 2013 [updated 2024]. Available from: https://www.nice.org.uk/guidance/qs35 [Accessed May 2026].

Recommended Reading

• NICE NG133 – Hypertension in pregnancy
• NICE DG49 – PlGF-based testing
• MBRRACE-UK – Saving Lives, Improving Mothers’ Care
• Action on Pre-eclampsia (APEC)