270. Acetylsalicylic acid for inhibition of platelet aggregation during pregnancy

Introduction Acetylsalicylic acid (ASA) is used as prevention against several obstetric complications. The efficacy of ASA on inhibition of platelet aggregation is well-known, but the effective dose of ASA during pregnancy is under debate. Objective/hypothesis We hypothesized that the inhibition of platelet aggregation by ASA is similar during the three trimesters of pregnancy. Methods Platelet aggregation was studied in women with recurrent miscarriage treated with ASA 75 mg (group A, n = 176) or placebo (group B, n = 177) and in healthy women with normal pregnancy (group C, n =  79). Platelet aggregation was detrmined with multiple elctrode impedance aggregometry (Multiplate, ASPI test, Roche Diagnostics International Ltd, Switzerland) before conception, during the three trimesters of pregnancy and postpartum. Results Mean values (SD) of the ASPI test before conception, available in groups A and B were 68.7U (25.7) and 75.1U (27.7), (p = 0.026). Platelet aggregation was markedly inhibited during pregnancy, but the inhibition decreased over the trimesters in group A. The ASPI tests were 12.8U (9.3), 19.2U (16.7) and 26.5U (23.1) in gestational weeks 13, 30 and 36 (p  The women treated with placebo and the healthy pregnant women presented only minor decrease in platelet aggregation during pregnancy. There were no differences between group B and C and no changes over time in these groups. Discussion Inhibition of platelet aggregation by ASA decreased as pregnancy continued. This can be a result of changes in plasma volume and increased turn-over of platelets. It is likely that the ASA dose has to be increased if the same inhibition of platelet aggregation by ASA is to be achieved during all three trimesters.