INCREASED WHOLE-BLOOD PLATELET-AGGREGATION IN NORMAL-PREGNANCY CAN BE PREVENTED INVITRO BY ASPIRIN AND DAZMEGREL (UK38485)

Objective To determine the effect of normal pregnancy and the early puerperium on whole blood platelet aggregation and to assess the role of thromboxane A2 (TXA2) in platelet aggregation in pregnancy. Design A prospective descriptive study. Setting TCD Medical School, St James's Hospital, Dublin. Subjects Twenty healthy primigravidae who remained normotensive during pregnancy and the puerperium. Interventions 20 ml blood samples were obtained serially at 12, 20, 28, 32 and 36 weeks gestation, during established labour and at 1 h, 24 h, 48 h and 6 weeks after delivery. Main outcome measures Whole blood platelet aggregation in response to aggregating agents ADP, PAF (platelet aggregating factor) collagen, adrenaline and arachidonic acid (AA) at each stage of pregnancy and peuerperium was measured using a particle counting technique. The in vitro effect of aspirin and dazmegrel (thromboxane synthetase inhibitor UK38485) on platelet aggregation in pregnancy was also investigated. Results Platelet aggregation in response to collagen, adrenaline, ADP and AA were increased in the last trimester, during labour and at 1 h after delivery but decreased 24-48 h after delivery. Platelet aggregation in response to AA, collagen and adrenalin was reduced by both aspirin and dazmegrel. Conclusions The earliest and most marked increases in platelet aggregation during normal pregnancy were found in response to AA and collagen. These platelet changes were prevented when whole blood was pre-incubated with either aspirin or dazmegrel. This suggests that enhanced production of TXA2 is responsible for increased platelet reactivity in normal pregnancy.