- Design
- Observational before-and-after cohort, single health system
- Population
- 36,914 deliveries at Parkland Health, 2020 to 2025
- Primary outcome
- Preeclampsia with severe features
- Effect
- 6.9% vs 5.1%; aOR 0.65 (95% CI 0.60 to 0.72)
Parkland Health in Texas changed policy in August 2022: every patient starting antenatal care by 16 weeks was given 162 mg aspirin daily, dispensed directly in clinic, regardless of risk factors. Before that date aspirin was not recommended at all. The team compared 18,457 deliveries in each epoch, excluding a six-month washout.
Preeclampsia with severe features fell from 6.9% to 5.1% (adjusted OR 0.65, 95% CI 0.60 to 0.72). Onset was later in the aspirin epoch, and the association held in women with chronic hypertension (aOR 0.72, 0.59 to 0.86). Abruption, postpartum haemorrhage and neonatal complications did not rise. Pharmacy records confirm at least 80.4% of eligible patients received aspirin, median 180 tablets.
This matters because risk-factor screening misses many who go on to develop pre-eclampsia, and screening itself is where programmes leak. The comparison is before-and-after, not randomised: other changes over 2020 to 2025, including the tail of the pandemic, could account for part of the difference. The baseline hypertensive rate here is high, so the absolute gain will be smaller where pre-eclampsia is rarer.
For services with a high burden of hypertensive disease and patchy screening, including many Indian public hospitals, universal low-dose aspirin started before 16 weeks is a defensible policy to discuss. Direct dispensing, not just prescribing, appears to be what made uptake high.
- Check booking gestation: the policy applied only to those starting care by 16 weeks.
- Dose used was 162 mg daily, higher than the 75 to 81 mg still common in practice.
- Record adherence at each visit; tablets dispensed is not tablets taken.
- Continue to ask about bleeding history and aspirin allergy before starting.
- If proposing a unit policy, audit severe pre-eclampsia and PPH rates before and after.
Why it matters
The weak link in aspirin prophylaxis is identifying who should get it; a universal policy removes that step.
Don't overread it
This was a before-and-after cohort, not a trial — secular trends may explain part of the fall.
The statistics, in plain English
An adjusted odds ratio of 0.65 means about a third lower odds of severe pre-eclampsia after the policy, after accounting for measured differences between the two groups. The absolute fall was 1.8 percentage points, so roughly 55 women needed aspirin for one fewer case. The narrow interval reflects the large numbers, not freedom from bias: a tight estimate from a non-randomised design can still be tightly wrong.
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