The use of chemical analyses of umbilical cord blood for the computation of instantaneous fetal growth

From the umbilical veno-arterial differences in the concentrations of carbohydrates, lipids and amino acids, and of oxygen, carbon dioxide and urea, one can calculate what fractions of the three fuels are burned and what fractions are deposited and constitute growth of the fetus. If umbilical blood flow is also measured, it is possible to calculate the instantaneous rate of fetal growth. Blood can be sampled from the umbilical artery and vein by means of indwelling catheters in unanesthetized sheep. Measurements of umbilical blood flow in unanesthetized sheep are available also. Application of the proposed analysis to published cord blood values for the fetal lamb lead to a predicted rate of growth that was in good agreement with the observed rate of growth. It also showed that a small uptake of a lipid like fuel is still being overlooked. It is concluded that analysis of a set of cord blood samples makes possible a calculation of the fraction of fuel uptake of the fetus that is being used for growth, at the time the samples were taken.