Red cell aggregation during normal pregnancy

Red cell aggregation (RCA) is responsible for the increase in whole blood viscosity at lower shear rates. RCA depends on the concentrations of red cells and plasma proteins with a high molecular weight and a large and asymmetrical spatial structure such as fibrinogen, immunoglobulin M and alpha 2-macroglobulin. During normal pregnancy, changes occur in all these concentrations. In a prospective study these changes and their influence on the resulting RCA were investigated in 24 healthy women with normal pregnancies. RCA was determined by light reflection measurement (syllectometry). RCA considerably increased during normal pregnancy in spite of the physiological haemodilution. The aggregation half time, used as a measure for RCA, decreased from an average non-pregnant value of 5.6 s to 3.3 s at 37 weeks. Multiple regression analysis showed that the increase in RCA could be mainly attributed to the raised fibrinogen concentration. However, at 37 weeks other factors, in addition to fibrinogen, contribute significantly to the increase in RCA.