MATERNAL SERUM THROMBOXANE B-2 CONCENTRATIONS DO NOT PREDICT IMPROVEDOUTCOMES IN HIGH-RISK PREGNANCIES IN A LOW-DOSE ASPIRIN TRIAL

OBJECTIVE: The aim of the study was too determine whether, in a low-do se aspirin trial in high-risk pregnancies, a decrease in maternal seru m thromboxane B-2 level predicted improved pregnancy outcomes. STUDY D ESIGN: This multicenter, randomized, double-blind trial included 2539 women, 1010 of whom had sufficient serum samples at enrollment and at 24 to 28 weeks' gestation, 34 to 38 weeks' gestation, or both to asses s longitudinal changes in thromboxane B-2 level and their effects on p regnancy outcomes. Women were randomly assigned between 13 and 26 week s' gestation to receive daily aspirin (60 mg) or placebo. RESULTS: Ove rall and in all subgroups women assigned to receive aspirin had marked ly lower maternal thromboxane B-2 concentration values than did those assigned to receive a placebo (P = .0001). Changes in thromboxane leve ls were not, however, correlated with adverse pregnancy outcomes. Wome n with greater than or equal to 50% reduction in maternal serum thromb oxane B-2 concentrations from baseline had occurrences of preeclampsia (P = .922), preterm birth (P = .375), small for gestational age neona tes (P = .938), and grade III or IV intraventricular hemorrhage (P = 1 .000) similar to those of women who had <50% reduction. Similar result s were found for women with thromboxane B-2 level decreases of <15 ver sus >15 ng/mL and women with thromboxane B-2 level decreases to <10 ve rsus greater than or equal to 10, <5 versus greater than or equal to 5 , and <1 versus greater than or equal to 1 ng/mL. Maternal thromboxane B-2 concentrations at enrollment were also not predictive of adverse outcomes. CONCLUSION: Neither maternal serum thromboxane B-2 concentra tions at enrollment nor their subsequent reduction were predictive of adverse pregnancy outcomes in a low-dose aspirin trial.