Changes of hemorheologic properties during normal human pregnancy.

To investigate alterations of hemorheologic properties during pregnancy, we measured the hematocrit (Hct) and fibrinogen levels, blood viscosity, and erythrocyte deformability in 10 healthy nonpregnant women and in 10 women with uncomplicated pregnancies. The Hct decreased during pregnancy, while the plasma fibrinogen concentration was elevated. No significant changes in blood viscosity were observed throughout pregnancy. Erythrocyte deformability was significantly decreased in pregnancy when compared to the nonpregnant state, but returned to the nonpregnant level by the 7th postpartum day. These findings suggest that adequate microcirculation is maintained in the uteroplacental unit during gestation by hemodilution, which prevents an elevation of blood viscosity despite the increase in fibrinogen and the decrease of erythrocyte deformability. These changes are thus thought to be among the physiological maternal adaptations to fetal growth and development.