Physiological modifications of blood viscosity and red blood cell aggregation during labor and delivery

Abstract

Since most stresses are known to modify blood rheology, we studied hemorheological parameters during labor and delivery, which are highly stressful physiological events. In 80 pregnant women we measured blood viscosity, plasma viscosity and red blood cell (RBC) aggregation during labor (before and after 4 cm dilatation), during delivery, and during delivery of the placenta. Blood viscosity at both native and corrected hematocrit increases (p<0.001) with a peak during delivery followed by a rapid normalization during delivery of the placenta (p<0.01). Hematocrit and plasma viscosity do not change during labor and delivery, but decrease during delivery of the placenta. RBC aggregation (physiologically increased during late pregnancy) acutely returns to normal during delivery (p<0.01). The transient increase in viscosity during delivery is explained by an increase in RBC rigidity as measured by Dintenfass ‘Tk’ (p<0.01) and a similar (nonsignificant) tendency to decrease RBC filterability measured by the hemorheometre. Thus, delivery is associated with a transient hyperviscosity syndrome which is mainly due to a decrease in RBC flexibility.