Prospective longitudinal study of thromboelastography and standard hemostatic laboratory tests in healthy women during normal pregnancy.

BACKGROUND: Hemostatic disorders are common in obstetric complications. Thromboelastography (TEG®) simultaneously measures coagulation and fibrinolysis within 10 to 20 minutes. Our primary aim in this prospective longitudinal study was to obtain knowledge about physiological changes in TEG® variables during normal pregnancy and 8 weeks postpartum. The secondary aims were to compare TEG® variables during pregnancy with TEG® variables 8 weeks postpartum and gestational weeks 10 to 15 and to correlate TEG® variables to standard laboratory analyses.
METHODS: Blood samples were collected from 45 healthy pregnant women at gestational weeks 10 to 15, 20 to 22, 28 to 30, and 38 to 40, and at 8 weeks postpartum. The following TEG® analyses were performed: time until start of clotting (TEG®-R), time until 20-mm clot firmness (TEG®-K), angle of clotting (TEG®-Angle), maximum amplitude (TEG®-MA), and lysis after 30 minutes (TEG®-LY30). Activated partial thromboplastin time, prothrombin time, soluble fibrin, antithrombin, D-dimer, and platelet count were analyzed.
RESULTS: Compared to 8 weeks postpartum TEG®-R was at least 0.9 minutes shorter (upper limit 99% confidence intervals) until gestational weeks 28 to 30 and the mean reduction varied between 23%-26%. TEG®-K was at least 0.1 minutes shorter throughout pregnancy and the mean reduction varied between 18%-35%. TEG®-Angle was at least 2.5 degrees greater during pregnancy and the mean increase varied between 12%-20%. TEG®-MA was also at least 0.4 mm greater during pregnancy and the mean increase varied between 6%-8%. TEG®-LY30 was at least 0.03% lower during gestational weeks 28 to 30 and 38 to 40 and the mean reduction varied between 67%-73%. The routine coagulation laboratory values were within normal pregnant limits. There were no or weak correlations between TEG® and the laboratory variables.
CONCLUSIONS: TEG® demonstrates increased coagulability and decreased fibrinolysis during pregnancy. There was a faster initiation of hemostasis, with a minor increase in clot strength. Fibrinolysis decreased during late pregnancy. Alternative cutoff limits for TEG® variables may be required during pregnancy. Standard hemostatic laboratory tests were as expected during pregnancy. Future studies are needed to ascertain whether viscoelastic methods are preferable to standard hemostatic tests for the diagnosis of coagulopathy during obstetric hemorrhage.