Previous studies from randomized trials have demonstrated that early administration of aspirin reduces the risk of preeclampsia. The effectiveness of prophylaxis with aspirin may be related to the time of its administration during gestation. A recent study reported that initiation of aspirin therapy before 16 weeks of gestation reduced the risk of the disease, but starting therapy after 16 weeks was ineffective. These data suggest that early administration of aspirin may be more effective for preventing preterm versus term preeclampsia.
The aim of this systematic review and meta-analysis was to investigate the benefits of low-dose aspirin started at or before 16 weeks of gestation and to examine its effect on the risk of preterm and term preeclampsia in women at risk. Data from prospective, randomized controlled trials in articles cited from 1965 through October 2011 were obtained from EMBASE, PubMed, the Cochrane Central Register of Controlled Trials, and Web of Science. All subjects in included studies had been randomized to low-dose aspirin or placebo/no treatment at or before 16 weeks of gestation. The primary outcome measures were preterm preeclampsia (delivery ≤37 weeks) and term preeclampsia. Pooled relative risks (RRs) were calculated.
Of the 7941 citations identified in the search, only 5 trials with a combined total of 556 women met inclusion criteria. Compared with controls, low-dose aspirin administered at or before 16 weeks of gestation was associated with a significant reduction in the risk of preterm preeclampsia (RR, 0.11; 95% confidence interval, 0.04–0.33). In contrast, early use of aspirin was not associated with a significant reduction in the risk of term preeclampsia (RR, 0.98; 95% confidence interval, 0.42–2.33).
These findings show that prophylaxis with low-dose aspirin initiated at or before 16 weeks of gestation reduces the risk of preterm but not term preeclampsia.