Who still develops preterm pre-eclampsia despite low-dose aspirin

Design

Secondary analysis of a multicentre stepped-wedge cluster randomised trial

Population

2919 women with singleton pregnancies at high risk of preterm pre-eclampsia, all on low-dose aspirin

Primary outcome

Predictors of preterm pre-eclampsia and time to delivery with pre-eclampsia

Effect

Preterm PE 3.7%; chronic hypertension aOR 1.835 (1.070 to 3.146); MAP MoM above 1.149 aOR 2.162 (1.434 to 3.261)

This is a secondary analysis of a stepped-wedge cluster randomised trial across 18 maternity and diagnostic units in 10 Asian regions. It included 2919 women with singleton pregnancies judged high risk for preterm pre-eclampsia (estimated risk of 1 in 100 or higher on the first-trimester Fetal Medicine Foundation triple test) who then received low-dose aspirin.

Overall 280 women (9.6%) developed pre-eclampsia and 107 (3.7%) developed preterm pre-eclampsia. Chronic hypertension (adjusted OR 1.835, 95% CI 1.070 to 3.146) and mean arterial pressure above 1.149 multiples of the median (aOR 2.162, 1.434 to 3.261) were associated with preterm disease. Risk rose steeply with the initial estimate: against the 1 in 51 to 1 in 100 band, the 1 in 2 to 1 in 5 band had an aOR of 15.845 (8.166 to 30.746).

These are associations within a treated, already high-risk group, and there was no comparison with unscreened or untreated women. They suggest where residual risk sits, which may help decide who needs closer surveillance after aspirin is started.

• Women with chronic hypertension or a raised first-trimester MAP stay at higher risk of preterm pre-eclampsia on aspirin.
• The higher the first-trimester estimated risk, the higher the residual risk; the top band was about sixteen times the lowest band.
• Consider tighter blood pressure and symptom surveillance for these women; this analysis does not test any specific surveillance plan.
• Aspirin is not a guarantee; counsel women that pre-eclampsia can still occur.
• Record MAP and chronic hypertension status at booking so risk can be reviewed later.

Why it matters

It shows that a high-risk screen result does not end with starting aspirin; some women remain clearly more exposed.

Don't overread it

This is a secondary, observational analysis of a trial, with no untreated comparison, so it cannot show whether aspirin dose or timing should change.

The statistics, in plain English

An adjusted odds ratio of 15.8 with a confidence interval of 8.2 to 30.7 is a large association, but the interval is wide because few women sat in the extreme band. The 1 in 21 to 1 in 50 band had a confidence interval spanning 1 (0.722 to 2.499), so no difference from the reference group was shown.

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