RESUMO
OBJECTIVE: Daily aspirin, started in the first trimester of pregnancy, is commonly used for the prevention of preeclampsia and fetal growth restriction in multiple gestation. However, the optimal dose remains controversial and the evidence for the use of aspirin in multiple pregnancies is scarce. We aimed to estimate the impact of 80 mg of aspirin in twin pregnancies. STUDY DESIGN: We performed a pilot double-blind randomized trial of women with twin pregnancies recruited between 8 and 14 weeks of gestation. Fifty participants (25 in each group) were randomized to 80 mg of aspirin daily at bedtime or a placebo from randomization until 36 weeks of gestation. Primary and secondary outcomes included the birth weight of live infants, preeclampsia, and aspirin responsiveness evaluated by a platelet aggregation test (platelet function assay [PFA]-100). RESULTS: All participants were followed until birth, including 48 and 47 live newborns in the aspirin and the placebo groups, respectively. The mean birth weight difference between the aspirin (2,385 ± 529 g) and placebo (2,224 ± 706 g) groups was of 179 g (95% confidence interval [CI]: -172-531 g, p = 0.32). We observed two (8%) cases of preeclampsia in the aspirin group and no case with placebo (p = 0.49). Most importantly,16 of 24 participants who received aspirin (67%; 95% CI: 45-84%) had a normal PFA-100 test at 22 to 23 weeks, including the two cases of preeclampsia, suggesting that the majority of the participants were nonresponsive to 80 mg of aspirin. CONCLUSION: Our results suggest that the majority of women with twin pregnancies showed a lack of response to a daily dose of 80 mg of aspirin according to the PFA-100 test, compared with the expected 29% of nonresponsiveness in singleton pregnancies. A daily dose of 80 mg of aspirin is likely to be insufficient for the prevention of preeclampsia and other placenta-mediated complications in twin pregnancies. KEY POINTS: · Most women with twin pregnancies are nonresponsive to a daily dose of 80-mg aspirin.. · An 80 mg aspirin dose is insufficient to prevent placenta-mediated complications in twin pregnancies.. · Randomized trials using 100 to 160 mg of aspirin in twin pregnancies are needed..