In the capillary areas erythrocyte deformability plays a significant part in determining perfusion and exchanges between blood and tissues. In fact, in the capillary areas, when the perfusion pressure diminishes, the erythrocytes no longer follow their linear trajectory movement but proceed randomly, thus favouring the phenomena of aggregation. In pregnancy we find a physiological haemodilution consequent upon the proportionally greater increase in the plasmatic volume in respect to the cellular one. In physiological conditions such haemodilution reaches equilibrium between the plastic and cellular components which, according to data shown would favor erythrocytic distortion and consequently the perfusion of the peripheral areas. The deformability expressed by VRBC increases up to the 26th-28th week of pregnancy, then remains constant until full term.