Blood viscosity factors and fetal erythrocyte aggregability were investigated
with light transmission (Myrenne device) during a cross‐sectional study of blood
drawn in utero by cord venepunctures in 119 normal fetuses between 18 and 39
weeks gestation. There was a progressive increased blood viscosity at native
hematocrit (
p<{}
0.01) explained by a gradual
increase in both hematocrit (from 33% to 40%,
p<{}
0.05) and Dintenfass’ ‘Tk’ RBC
rigidity index (
p<{}
0.05), while plasma viscosity
remained constant at 1.18 ± 0.01 mPa.s as well as the
h/&eegr; ratio (188.4
± 2.7
mPa<formula>^{-1}
.s
^{-1}
). The RBC
aggregation index ‘M’ remained almost equal to zero (mean value: 0.04 ± 0.01)
before 32 wk gestation and then increased (
p<{}
0.05) until delivery. The
upper physiological limit for this parameter before 32 wk (mean ± 2 SD) is 0.18.
The RBC aggregation index ‘M1’ remained constant during pregnancy at 2.98 ±
0.26, i.e., the upper physiological limit for this parameter during the
intrauterine life (mean ± 2 SD) is 7.85. Both fibrinogen (
r={}
0.479,
p<{}
0.05) and
albumin (
r={}
0.494,
p<{}
0.01) correlated with time so
that the albumin/fibrinogen ratio remained stable. We then studied with the
laser retrodiffusion technique the venous blood of 20 women (18–43 yr, 37–40 wk
gestation) and the cord blood of their newborns at birth, comparing RBC
aggregation of: mothers (M), maternal RBCs resuspended on newborn plasma (MF),
newborn RBCs resuspended on maternal plasma (FM), and newborns (F).
Aggregability is higher in M (RBC aggregation time M
{}<{}
MF
{}<{}
FM
{}<{}
F;
p<{}
0.01); RBC
aggregation index at 10 s M
{}>{}
MF
{}>{}
FM
{}>{}
F;
p<{}
0.01), with in
turn the symmetric inverse picture for the partial disaggregation threshold
(M
{}>{}
MF
{}={}
FM
{}>{}
F). Thus RBC
disaggregability is higher in newborns, and suspensions on maternal and newborn
plasma suggest that half of this difference in aggregability (and
disaggregability) between fetal and adult blood results from plasma factors and
another half from erythrocytes.
