Low-dose aspirin reduces preterm pre-eclampsia in women at high risk, but the benefit is concentrated where it is started before 16 weeks. A woman flagged at her first visit who is not started on aspirin until the anomaly scan has largely missed the window.
Most national guidance recommends 75-150 mg daily from 12 weeks for women with a high-risk factor, such as previous pre-eclampsia, chronic hypertension, chronic kidney disease, autoimmune disease or diabetes, or with two or more moderate risk factors. Many units give it at night, and adherence is the main reason it fails.
- Assess pre-eclampsia risk at the booking visit, not later.
- Start low-dose aspirin from 12 weeks, and before 16 weeks, in women at high risk, following your national guidance on dose.
- Check adherence at each visit; missed doses are common.
- Combine aspirin with closer blood pressure surveillance rather than relying on it alone.
Why it matters
The commonest failure is not the drug but the start date.
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