Abstract
The physiological weight loss in the newborn has been related to the elimination and the low ingestion of liquids in the first days oflife. The degree of weight loss, generally less than 10% of the birth weight, is related to the resolution in higher or lesser degree of neonatal edema and an adequate administration of liquids to the newborn. The following study was done to test the hypothesis that the physiological weight loss in the newborn could be related to homeostatic situations before delivery, which would determine the fluid balance in the first few days of life. We analyzed the relationship between plasma viscosity and blood density of cord blood with weight loss in the first 48 hours of life. Twenty-six healthy newborns of gestational ages between 259 and 296 days (278 ± 8, mean ± SD) were studied. The following parameters were determined in the umbilical artery and vein: haematocrit, blood density, plasma viscosity and osmolality. Blood gas parameters were determined using a blood gas analyzer. We determined the weight of the newborn at birth and after 48 hours. We did not find significant differences between the arterial and venous blood densities, with a density in the umbilical artery of 1.05 ± 0.01 g/ml and 1.06 ± 0.03 g/ml in the umbilical vein. The weight loss in the first 48 hours in the newborn was 151 ± 80.8 g, with a birth weight of 3325 ± 414 g. Our results suggest that decrease of body liquid volume in the fetus is accompanied by an increase in plasma viscosity which could produce a decrease of the neonatal diuresis with less physiological weight loss in the newborn after delivery. This event is related to a decrease offetal plasma bicarbonate.
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