Fifteen RCTs (eight good quality) of high-risk women were included in the review, along with six RCTs and two observational studies (seven good quality) of average-risk women to assess harms.
Benefits of low-dose aspirin treatment
Data from 10 trials (12,240 participants) suggested a statistically non-significant reduction in perinatal death (RR 0.81, 95% CI 0.65 to 1.01; Ι²=0%).
Pooled data from 10 trials (11,779 participants) suggested a statistically significant reduction in pre-term birth (RR 0.86, 95% CI 0.76 to 0.98; Ι²=33%).
There was evidence of a statistically significant reduction in inter-uterine growth restriction (RR 0.80, 95% CI 0.65 to 0.99; Ι²=36%) from 13 trials (12,504 participants).
Average birthweight was greater in aspirin treated groups (130g, 95% CI 36.2 to 223.3; Ι²=60%) and preeclampsia was reduced (RR 0.76, 95% CI 0.62 to 0.95; Ι²=41%; 13 trials; 12,184 participants).
There was evidence of small-study effects for pre-term birth, inter-uterine growth restriction and preeclampsia; larger studies reported smaller and statistically non-significant effects. Prediction intervals suggested that future studies could shift statistically significant pooled estimates towards non-significance.
Harms of aspirin treatment
No statistically significant harm for perinatal death, placental abruption, postpartum haemorrhage, mean blood loss, or neonatal intracranial haemorrhage was found. However, event rates were generally low, which increased uncertainty.
Details of sensitivity analyses were reported in the paper.