Aspirin for Prevention of Pre-eclampsia

Low-Dose Aspirin for Prevention of Pre-eclampsia (Pregnancy-Induced Hypertension Spectrum Disorders)

https://www1.racgp.org.au/ajgp/2022/october/indications-for-commencing-aspirin

Why use aspirin?

• Hypertensive disorders of pregnancy are a major cause of maternal, fetal and neonatal morbidity and mortality.
• Low-dose aspirin (LDA) reduces the risk of pre-eclampsia when commenced early in pregnancy.
• Women with previous pregnancy-induced hypertension have approximately:
  • 20% recurrence risk in future pregnancies.
  • Higher risk if previous pre-eclampsia required delivery before 37 weeks.

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Who should receive aspirin?

Start low-dose aspirin if:

At least ONE high-risk factor OR TWO or more moderate-risk factors are present.

High-risk factors

• Previous pregnancy complicated by:
  • Gestational hypertension
  • Pre-eclampsia
  • HELLP syndrome
• Chronic hypertension
• Type 1 or Type 2 diabetes
• Chronic kidney disease
• Autoimmune disease:
  • Systemic lupus erythematosus (SLE)
  • Antiphospholipid syndrome
  • Scleroderma
• Multifetal pregnancy (twins/triplets)
• Assisted conception with oocyte donation

Moderate-risk factors

• First pregnancy (primigravida)
• Maternal age:
  • ≥35 years (some guidelines)
  • ≥40 years (higher risk)
• Pregnancy interval >10 years
• BMI >30 kg/m²
  • Some guidelines use BMI >35 kg/m²
• Family history of pre-eclampsia
  • Mother or sister affected
• Low socioeconomic status
• Personal history of low birth weight
• Previous adverse pregnancy outcomes
• Multifetal pregnancy (included as moderate risk in some guidelines)

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Dose and Timing

Recommended dose

• Aspirin 100–150 mg daily

When to start

• Ideally before 16 weeks gestation
• Preferably from 12 weeks gestation
• Greatest benefit occurs when started early.

If started later

• Some benefit still seen if commenced up to 28 weeks gestation.

When to stop

• Current recommendations:
  • Continue until birth
  • No longer routinely stopped at 36 weeks

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Effectiveness

• Relative risk reduction:
  • RR 0.76 (95% CI 0.62–0.95)
• Number needed to treat (NNT):
  • Approximately 42–70 women to prevent one case of pre-eclampsia.

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Safety

Evidence shows no significant increase in:

• Placental abruption
• Postpartum haemorrhage
• Neonatal haemorrhage
• Congenital anomalies
• Premature ductus arteriosus closure

Regional anaesthesia

• Low-dose aspirin is not a contraindication to epidural or spinal anaesthesia.

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Contraindications

Avoid aspirin in patients with:

• Aspirin-exacerbated respiratory disease (Samter’s triad)
• Active peptic ulcer disease
• Gastrointestinal bleeding
• Genitourinary bleeding
• Significant hepatic dysfunction
• True aspirin allergy

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Other Preventive Measures

Calcium supplementation

• Calcium 500 mg daily started early in pregnancy may reduce pre-eclampsia risk, particularly:
  • High-risk women
  • Women with low dietary calcium intake

Not recommended for prevention

• Magnesium supplements
• Vitamin C
• Vitamin E

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Important Clinical Pearls for GPs

• Assess all pregnant women at their first antenatal visit for pre-eclampsia risk factors.
• Do not wait for obstetric review before initiating aspirin if criteria are met.
• Aspirin is recommended for prevention of pre-eclampsia, not for:
  • Isolated fetal growth restriction
  • Unexplained stillbirth
  • Other obstetric complications in the absence of pre-eclampsia risk factors.
• Early commencement (12–16 weeks) provides the greatest benefit