Study designs of evaluations included in the review
Double-blinded randomised controlled trials (RCTs) with appropriate concealment of allocation were eligible for inclusion.
Specific interventions included in the review
Studies of low-dose aspirin administered for the prevention of pre-eclampsia, compared with placebo, were eligible for inclusion. The dose of aspirin ranged from 60 to 100 mg/day in low-risk women and from 50 to 150 mg/day in high-risk women.
Participants included in the review
Women at low risk or high risk of developing pre-eclampsia were eligible for inclusion. The criteria for identifying women at high risk of pre-eclampsia were one or a combination of the following risk factors and tests.
Risk factors: essential chronic arterial hypertension prior to the pregnancy, insulin-treated diabetes, or an antecedent of severe pre-eclampsia (eclampsia, HELLP syndrome, blood-pressure of 160/110 mmHg, imminence of eclampsia, respiratory distress or renal failure).
Tests: positive tests such as Doppler ultrasonography, the rollover test, or the angiotensin II sensitivity test.
Women at low risk were those without any of the above risk factors or tests. Trials with mixed populations were excluded. The gestational age of women in the trials ranged from 12 to 32 weeks in low-risk women and from 12 to 33 weeks in high-risk women.
Outcomes assessed in the review
Studies reporting data on the incidence of pre-eclampsia were eligible for inclusion. Pre-eclampsia was defined as increasing blood-pressure after 20 gestational weeks that was associated with proteinuria of at least 300 mg per 24 hours.
How were decisions on the relevance of primary studies made?
Two reviewers independently assessed the studies for inclusion, but the authors did not state how any disagreements were resolved.