THE VARIATION WITH GESTATIONAL-AGE OF THE RHEOLOGICAL PROPERTIES OF THE BLOOD OF THE NEWBORN

A study has been made of the variation of blood viscosity and related factors with the gestational age of neonates from 24 weeks to normal term. Viscosity increases significantly over this period by 36% at high shear rate (128.5 s(-1)) and 250%, at low shear(0.277 s(-1)). The high shear rate changes can be explained largely by the effects of variations in haematocrit and plasma viscosity. At low shear rate the same factors are involved together with changes in the plasma protein composition, in particular the age-related increase in the concentration of the proteins known to induce rouleaux formation. The variation in the degree of sialination of fibrinogen with gestational age may also play a part.