On changes in aggregation of red cells,blood viscosity and plasma viscosity during normal gestation

Abstract

Haemorheological factors (blood viscosity, plasma viscosity, aggregation of red cells, rigidity of red cells) and biochemical factors (fibrinogen, albumin, cholesterol) were studied in 32 healthy women during normal pregnancies. Plasma viscosity was low, but increased with progress of gestation. Aggregation of red cells was very high, and fibrinogen was increased, while both parameters increased significantly with gestation time. Haematocrit and blood viscosity (measured at shear rate of 180 sec⁻¹ ) decreased during the first half of pregnancy, but increased progressively during the second half of pregnancy. Some viscosity factors during the last weeks of gestation were not only significantly higher than the normal values, but were significantly increased above the values observed during the earlier stages of pregnancy. In particular, during the last four weeks of gestation the values for aggregation of red cells were 252 ± 54 mm/hr, and for fibrinogen 423 ± 80 mg%. Thus, at least during the last stages of pregnancy, there existed a state of hyperviscosity. The following aspects are covered in discussion: inter-relation between blood pressure and blood viscosity, the role of increased blood volume, possible presence of a vasodilator substance counteracting effects of hyperviscosity, possible effect of hyperviscosity on foetus development, malformation, etc.