RESUMO
During pregnancy because of physiologic hemodiluition and changes in various plasma protein levels, plasma viscosity is decreased compared to the non pregnant condition. Specifically the whole blood viscosity profile throughout pregnancy follows that of the hematocrit. However some pathological condition like pregnancy induced hypertension and intrauterine growth retardation are characterized by an increase of plasma viscosity. In order to evaluate the effect of plasma viscosity on placental perfusion, in 41 patients affected by pregnancy induced hypertension and with no iron deficiency we compared maternal hemoglobin and hematocrit to the birth weight. High maternal hemoglobin and hematocrit levels were associated to an increased frequency of low weight for date newborns (less than or equal to 10th centile), although the relationship with the hemoglobin levels is stronger (p less than or equal to 0.02) than the one with the hematocrit (p less than or equal to 0.05). In contrast, high weight for date newborns (greater than or equal to 90th centile) were not related to maternal hemoglobin and hematocrit parameters. We found that maternal hemoglobin and hematocrit, indicators of plasma viscosity, are useful in predicting low birth weight, but not high birth weight. We speculate that hypoxia due to the modification of microcirculation is a very important factor in determining the low birth weight; in contrast the oxygen is not the only factor involved in determining the high birth weight.
