A Cochrane review included 59 studies with a total of 37 560 women. In 51 trials, aspirin alone was compared with placebo or no treatment. Of the remainder, five used a combination of aspirin and dipyridamole or dipyridamole alone versus control. Single small trials compared heparin and dipyridamole versus control, aspirin with vitamins C and E and fish oil or ozagrel hydrochloride with placebo. There was a 17% reduction in the risk of pre-eclampsia associated with the use of antiplatelet agents (RR 0.83, 95% CI 0.77 to 0.89; 46 trials, n=32 891); NNT 72 (95% CI 52 to 119). Antiplatelets were associated with an 8% reduction in the relative risk of preterm birth (RR 0.92, 95% CI 0.88 to 0.97; 29 trials, n=31 151); NNT 72 (95% CI 52 to 119), a 14% reduction in fetal or neonatal deaths (RR 0.86, 95% CI 0.76 to 0.98; 40 trials, n=33 098); NNT 243 (95% CI 131 to 1 666) and a 10% reduction in small-for-gestational age babies (RR 0.90, 95% CI0.83 to 0.98; 36 trials, n=23 638).
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