IPD from 31 RCTs (including IPD for 32,217 women and 32,819 babies) were included in the review. The authors stated that other eligible trials were identified, but in 7 of these it was not possible to trace the investigators; one trialist refused to participate, data from 17 trials were lost or irretrievable, and the investigators of 2 trials did not provide the data.
Twenty-six of the 31 included trials were judged to be good quality.
Compared with control treatment, antiplatelet agents were associated with a significantly lower risk of pre-eclampsia (relative risk, RR 0.90, 95% confidence interval, CI: 0.84, 0.97, p=0.004), delivery before 34 weeks (RR 0.90, 95% CI: 0.83, 0.98, p=0.011) or serious adverse outcomes during pregnancy (RR 0.90, 95% CI: 0.85, 0.96, p=0.001). There was no evidence of statistical heterogeneity for the outcome of pre-eclampsia (p=0.12, I-squared 26.3%). The authors calculated that 114 women had to be treated with an antiplatelet agent to prevent one case of pre-eclampsia. The overall results remained consistent when using the trialists' definition of pre-eclampsia (RR 0.88, 95% CI: 0.81, 0.96), or the PARIS (Perinatal Antiplatelet Review of International Studies) definition of pre-eclampsia (RR 0.90, 95% CI: 0.83, 0.97).
Mortality of the foetus or baby and the incidence of small for gestational age infants were comparable between antiplatelet agents and control groups. The use of antiplatelet agents was associated with a significantly lower risk (10%) of the combined outcome pre-eclampsia, delivery before 34 weeks' gestation, foetal or baby death before discharge, small for gestational age infant, and maternal death (RR 0.90, 95% CI: 0.85, 0.96).
Maternal outcomes such as proteinuria onset before 34 weeks, severe hypertension, placental abruption and Caesarean delivery did not differ between the intervention and control treatment.
Antiplatelet agents reduced the risk of pre-term birth before 37 weeks (RR 0.93, 95% CI: 0.89, 0.98, p=0.003) and the need for neonatal assisted ventilation (RR 0.79, 95% CI: 0.67, 0.95, p=0.010). It was estimated that 78 infants had to receive an antiplatelet agent through their mother to prevent one from needing assisted ventilation. The incidence of mother's or infant's bleeding events was similar between antiplatelet agents and controls.
Antiplatelet agents appeared to have similar benefits across the various predefined subgroups.