Erythrocyte deformability of nonpregnant, pregnant, and fetal blood.

Erythrocyte deformability is an important determinant of microcirculation, of oxygen transport and release to the tissue. In an attempt to clarify the rheological peculiarity during pregnancy, erythrocyte deformability was measured in 10 nonpregnant controls and 10 pairs of mothers and newborns. When the hematocrit of the erythrocyte suspension in dextran solution was adjusted to 35%, the deformability of fetal erythrocytes was significantly higher than maternal blood (P < 0.05), and it was almost similar to that of nonpregnant controls. Erythrocyte deformability was dependent on the hematocrit, and there was an optimal hematocrit value at which the deformability was maximal. The hematocrit, where the deformability was maximal, was a lower value (32-35%) in maternal blood, conversely, a higher value (47-50%) in cord blood than that (40-43%) in the nonpregnant. Despite decreased deformability of maternal erythrocytes, it may be compensated by reducing the hematocrit (hemodilution), preserving effective peripheral circulation including uteroplacental perfusion. On the other hand, the deformability of fetal erythrocytes may be higher in vivo at the hematocrit of 47-50% to supply oxygen to the fetal tissue even in a low oxygen condition.