ABSTRACT
The increase in blood viscosity during pregnancy reduces maternal-fetal blood flow, which can lead to fetal hypoxia and acidosis. These factors have been related to a reduction in fetal growth and to premature births. We carried out a longitudinal study of 36 normal-term gestations at different stages of the pregnancy. We analyzed the erythocyte deformability, the intraerythocyte viscosity and the plasma viscosity in the mother, as well as the relation of these parameters to fetal growth (biparietral diameter (BPD) and length of the femur), birthweight, gestational age at birth and the Agpar score. The results obtained were as follows: from weeks 25 to 36 of pregnancy (30.9 (SD 2 weeks)) there occurs a significant increase in maternal erythocyte rigidity (p < 0.05) (despite the compensatory decrease in intracellular viscosity). This increase is very significantly related to the fetal biparietral diameter (r = -0.50, p < 0.01), the length of the fetal femur (r = -0.48, p < 0.02), gestational age at birth (r = -0.73, p < 0.0001, birthweight (r = -0.63, p < 0.001) and the Agpar score 5 minutes after birth (r = 0.67, p < 0.001). Our conclusions are that the reduction in erythocyte deformability (which we attribute to alterations in the fluidity or elasticity of its membrane) and the factors that increase the aggregation capacity of the red cells (modulators of blood viscosity and of blood flow in the placental intervillous space) are risk factors for reduced fetal growth, lower birthweight and lower gestational age at birth. By avoiding maternal hematocrit levels higher than 36% we could improve uteroplacental perfusion, fetal growth and perinatal results.
