Platelet activation and placenta-mediated adverse pregnancy outcomes: an ancillary study to the EAGeR trial

Abstract Background Platelet activation may play a role in the pathophysiology of placenta-mediated obstetric complications, as evidenced by the efficacy of aspirin for preventing preeclampsia, but published data regarding the relationship between biomarkers for platelet activation and adverse obstetric outcomes are sparse. Specifically, it is unknown whether pre-pregnancy biomarkers of platelet activation are associated with adverse pregnancy outcomes. Objectives To determine: 1) whether maternal plasma concentrations of platelet factor 4 are associated with risk of placenta-mediated adverse obstetric outcomes, and 2) whether these associations are modified by low-dose aspirin. Study Design This ancillary study included measurement of platelet factor 4 among 1,185 of the 1,228 reproductive-age women enrolled in the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial with available plasma samples, with relevant outcomes assessed among 584 women with pregnancies lasting at least 20 weeks’ gestation. We measured platelet factor 4 in plasma samples obtained at the pre-pregnancy study visit (prior to randomization to low-dose aspirin or placebo), 12 weeks of gestation, and 28 weeks of gestation. The primary outcome was a composite of hypertensive disorders of pregnancy, placental abruption, and small-for-gestational age neonate. We estimated relative risks and 95% confidence intervals for the association between platelet factor 4 and the composite and individual outcomes at each time point using log-binomial regression that was weighted to account for potential selection bias and adjusted for age, BMI, education, income, and smoking. To evaluate potential effect modification by aspirin, we stratified analyses by aspirin treatment assignment. Results During follow-up, 95 women experienced the composite adverse obstetric outcome, with 57 cases of hypertensive disorders of pregnancy, 35 of small-for-gestational age (SGA), and 6 of placental abruption. Overall, pre-pregnancy platelet factor 4 was positively associated with the composite outcome (tertile 3 vs. tertile 1 RR 2.36, 95% CI 1.38, 4.03) and with hypertensive disorders of pregnancy (tertile 3 vs. tertile 1 RR 2.14, 95% CI 1.08, 4.23). In analyses stratified by treatment group, associations were stronger in the placebo (tertile 3 vs. tertile 1 RR 3.36, 95% CI 1.42, 7.93) versus the aspirin group (tertile 3 vs. tertile 1 RR 1.78, 95% CI 0.90, 3.50). Conclusions High concentrations of platelet factor 4 prior to pregnancy are associated with increased risk of placenta-mediated adverse pregnancy outcomes, particularly for hypertensive disorders of pregnancy. Aspirin may mitigate the increased risk of these outcomes among women with higher plasma concentrations of preconception platelet factor 4, but low-dose aspirin non-responders may require higher doses of aspirin or alternate therapies to achieve obstetric risk reduction.