Increased whole blood platelet aggregation in normal pregnancy can be prevented in vitro 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.