Author of editorial did not criticise studies' methodology

EDITOR—In her editorial discussing the value or otherwise of aspirin for preventing and treating pre-eclampsia Duley wonders why the small trials have such different results from the large trials.1 We suggest the following answer.

Evidence based medicine means integrating individual skill with the best available evidence from systematic research. Duley's conclusions, based on several multicentre studies, seem to rely on the conclusions of these studies without her making criticisms of the methodology used.

Firstly, the timing of the start of treatment with low dose aspirin is important. The studies consistently fail to show the percentage of women who were <16 weeks pregnant, the crucial time when maximum trophoblastic invasion is taking place (table). This issue was raised by de Swiet in Bower's news article2 and by Beaufilis et al.3

Secondly, the dose of aspirin used in the later large trials is low. A meta-analysis by Leitich et al (not quoted in the editorial) shows that aspirin was more effective at higher doses (100-150 mg/day) than at lower …