Dynamic parameters of maternal amino acid metabolism and fetal growth.

This study presents kinetic parameters of glycine metabolism during pregnancy and the influence of fuel availability on fetal growth. The kinetic studies were done on patients with gestational diabetes mellitus (diet treated) and pre-gestational diabetes mellitus (diet and insulin treated) that was accompanied by increased fetal growth and pregnancy-induced hypertension and, during the third trimester of pregnancy, by intrauterine growth retardation. Gas chromatography-mass spectrometry was used to determine the 15N enrichment of plasma glycine, and to calculate the pool sizes, turnover rate constants, fluxes and metabolic clearance rates. Glycine pool sizes in pre-gestational diabetes were significantly larger than those in normal, hypertensive and gestational diabetes pregnancies. Glycine turnover rate constants and metabolic clearance rates were not significantly different between the normal pregnant women, the hypertensive, and the two diabetic groups of pregnant women. Glycine fluxes were significantly higher in the pre-gestational diabetic pregnant women than in those with gestational diabetes, hypertension, and normal pregnancy. Pre-gestational diabetic pregnant women delivered fetuses with higher birthweights than the other three groups. Fetal birthweight of the hypertensive women was significantly lower than among the normal and diabetic women. Stable isotope methodology using labeled amino acids provides a powerful tool for clinical studies of maternal protein metabolism and its relationship to fetal growth.