Evidence of in vivo platelet activation during heparin anticoagulation in pregnancy for prophlaxis or treatment of thromboembolism.

ABSTRACT

Conventional unfractionated heparin substantially enhances spontaneous platelet aggregation in pregnancy in vitro, and may cause platelet activation in healthy volunteers in vivo. It is unknown, however, whether therapeutically administered heparin affects platelet behavior during pregnancy. In a parallel group ex vivo study, 8 third trimester pregnant patients requiring anticoagulation with heparin exhibited a trend to a greater spontaneous platelet aggregation, in comparison to 11 age-matched healthy third trimester pregnant controls. This is consistent with heparin-induced platelet activation in vivo during therapeutic anticoagulation. Peak aggregation in the heparin-treated group was 48 +/- 4% compared to 37 +/- 5% in the healthy controls, (P = 0.086 ANOVA) and significant time treatment interaction (P = 0.03 ANOVA). There was also a weak positive correlation (r = 0.54) between the peak % spontaneous platelet aggregation and the activated partial thromboplastin time ratio during heparin administration.