Background

Pre‐eclampsia is associated with deficient intravascular production of prostacyclin, a vasodilator, and excessive production of thromboxane, a vasoconstrictor and stimulant of platelet aggregation. These observations led to the hypotheses that antiplatelet agents, low‐dose aspirin in particular, might prevent or delay development of pre‐eclampsia.

Objectives

To assess the effectiveness and safety of antiplatelet agents for women at risk of developing pre‐eclampsia.

Search methods

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (July 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2005, Issue 1), EMBASE (1994 to November 2005) and handsearched congress proceedings of the International and European Societies for the Study of Hypertension in Pregnancy.

We updated the search of the Cochrane Pregnancy and Childbirth Group's Trials Register on 31 May 2010 and added the results to the awaiting classification section

Selection criteria

All randomised trials comparing antiplatelet agents with either placebo or no antiplatelet agent were included. Quasi‐random studies were excluded. Participants were pregnant women at risk of developing pre‐eclampsia. Interventions were any comparisons of an antiplatelet agent (such as low‐dose aspirin or dipyridamole) with either placebo or no antiplatelet.

Data collection and analysis

Two authors assessed trials for inclusion and extracted data independently.

Main results

Fifty‐nine trials (37,560 women) are included. There is a 17% reduction in the risk of pre‐eclampsia associated with the use of antiplatelet agents ((46 trials, 32,891 women, relative risk (RR) 0.83, 95% confidence interval (CI) 0.77 to 0.89), number needed to treat (NNT) 72 (52, 119)). Although there is no statistical difference in RR based on maternal risk, there is a significant increase in the absolute risk reduction of pre‐eclampsia for high risk (risk difference (RD) ‐5.2% (‐7.5, ‐2.9), NNT 19 (13, 34)) compared with moderate risk women (RD ‐0.84 (‐1.37, ‐0.3), NNT 119 (73, 333)).

Antiplatelets were associated with an 8% reduction in the relative risk of preterm birth (29 trials, 31,151 women, RR 0.92, 95% CI 0.88 to 0.97); NNT 72 (52, 119)), a 14% reduction in fetal or neonatal deaths (40 trials, 33,098 women, RR 0.86, 95% CI 0.76 to 0.98); NNT 243 (131, 1,666) and a 10% reduction in small‐for‐gestational age babies (36 trials, 23,638 women, RR 0.90, 95% CI0.83 to 0.98). There were no statistically significant differences between treatment and control groups for any other outcomes.

Authors' conclusions

Antiplatelet agents, largely low‐dose aspirin, have moderate benefits when used for prevention of pre‐eclampsia and its consequences. Further information is required to assess which women are most likely to benefit, when treatment is best started, and at what dose.

[Note: The 16 citations in the awaiting classification section of the review may alter the conclusions of the review once assessed.]