Risk Factors for Severe Pre-eclampsia
The strongest risk factors for developing pre-eclampsia are antiphospholipid antibodies (RR 9.72), previous pre-eclampsia (RR 7.19), pre-existing diabetes (RR 3.56), and multiple pregnancy (RR 2.93), with women having any of these factors requiring specialist referral before 20 weeks' gestation. 1
Highest-Risk Factors Requiring Early Specialist Referral
Women with the following factors should be referred before 20 weeks for specialist input to their antenatal care plan 1:
Single High-Risk Factors
- Previous pre-eclampsia (RR 7.19,95% CI 5.85-8.83) 1
- Antiphospholipid antibodies (RR 9.72,95% CI 4.34-21.75) - the strongest predictor 1
- Pre-existing diabetes mellitus (RR 3.56,95% CI 2.54-4.99) 1, 2
- Multiple pregnancy (RR 2.93,95% CI 2.04-4.21) 1
- Pre-existing hypertension or booking diastolic BP ≥90 mmHg 1, 2
- Pre-existing renal disease or booking proteinuria (≥+ on more than one occasion or ≥300 mg/24h) 1, 2
Two or More Moderate-Risk Factors
Women with any two of the following factors also require specialist referral 1:
Moderate-Risk Factors
- Nulliparity/first pregnancy (RR 2.91,95% CI 1.28-6.61) 1
- Family history of pre-eclampsia in mother or sister (RR 2.90,95% CI 1.70-4.93) 1
- Maternal age ≥40 years (RR 1.68 for nulliparous, RR 1.96 for multiparous women) 1
- Body mass index ≥35 kg/m² at booking (RR 1.55,95% CI 1.28-1.88) 1, 2
- Pregnancy interval ≥10 years since last baby 1
- Booking diastolic blood pressure ≥80 mmHg (but <90 mmHg) 1
- Receipt of assisted reproduction 1
Additional Risk Factors from Recent Evidence
- Chronic kidney disease - associated with increased risk and worse maternal outcomes 2
- Obesity (BMI >30 kg/m²) - broader definition than the BMI ≥35 threshold above 1, 2
Clinical Context and Pitfalls
The 2018 ISSHP guidelines emphasize that women with "established strong clinical risk factors" should receive low-dose aspirin (75-162 mg/d) ideally before 16 weeks but definitely before 20 weeks' gestation 1. This represents the most effective prevention strategy for preterm pre-eclampsia, though it does not prevent term pre-eclampsia 1.
Common pitfall: Failing to recognize that the presence of antiphospholipid antibodies confers nearly 10-fold increased risk - the highest of all risk factors - and mandates both specialist referral and aspirin prophylaxis 1.
Important distinction: Women with one moderate-risk factor require enhanced community monitoring (minimum 3-week intervals before 32 weeks, then 2-week intervals), while those with high-risk factors or two moderate-risk factors require specialist-led care from early pregnancy 1.
The risk assessment should occur early in pregnancy to allow timely initiation of aspirin prophylaxis and appropriate surveillance intensity 1. Women considered at increased risk should also receive supplemental calcium (1.2-2.5 g/d) if dietary intake is likely low (<600 mg/d) 1.