[Hemorrheological modifications during normal pregnancy].

Abstract

To investigate whole blood viscosity and its determinants during normal pregnancy we measured the changes in haematocrit, red cell aggregation, plasma viscosity and whole blood viscosity in 24 women during the course of their normal pregnancy. Red cell aggregation was measured by means of a syllectometer, plasma and whole blood viscosity by means of a Contraves LS 30 rotational viscometer. Red cell aggregation was found to increase during the whole course of normal pregnancy in spite of the physiological haemodilution. This increase could be attributed--to a great extent--to the increase in fibrinogen concentration during pregnancy. Plasma viscosity increased during the second and especially the third trimester of normal pregnancy, after a small decrease during the first trimester. Plasma viscosity represents a balance between the rising fibrinogen and the falling serum protein concentration. During normal pregnancy we found a decrease in whole blood viscosity at all shear rates until the 30th week, followed by a smaller increase between 30 and 37 weeks. The changes in whole blood viscosity were largely determined by the changes in haematocrit and to a smaller extent by the changes in plasma viscosity. The influence of plasma viscosity on the resulting whole blood viscosity increased at higher shear rates. At lower shear rates haematocrit was the most important determinant of whole blood viscosity. We did not find any influence of the increase in red cell aggregation on low shear blood viscosity as measured in a rotational viscometer. In our opinion the decrease in haematocrit during normal pregnancy not only compensates for the enhanced red cell aggregation, but even diminishes the resistance to flow in the intervillous space.(ABSTRACT TRUNCATED AT 250 WORDS)