Steady state maternal fetal leucine enrichments in normal and intrauterine growth restricted pregnancies

The aim of this study was to compare the fetal/maternal (F/M) leucine- enrichment ratio in normal (AGA) and intrauterine growth-restricted (IUGR) pregnancies at the time of fetal blood sampling (FBS). A maternal primed- constant infusion of L-[1-13C]-leucine was given in six AGA and 14 IUGR pregnancies, divided into three groups according to the pulsatility index (PI) of the umbilical artery and to fetal heart rate (FHR): group 1 (normal FHR and PI, four cases); group 2 (normal FHR and abnormal PI, five cases); and group 3 (abnormal FHP and PI, five cases). Maternal arterialized samples were taken at time zero and every 20 min for 125 ± 7 min. Umbilical venous samples were obtained after 114 ± 42 rain of infusion. Under steady state conditions, there was a significant linear relationship between maternal leucine disposal rate and maternal leucine concentration. The comparison of fetal to maternal leucine enrichment showed a progressive dilution of the fetal enrichment relative to the mother between AGA and IUGR of group 1 (0.89 versus 0.78, p < 0.02), group 2 (0.71, p <0.001), and group 3 (0.62, p < 0.001), and also among the three IUGR groups. The F/M leucine molar percent enrichment (MPE) ratio showed a positive correlation with the umbilical venous oxygen content and in inverse correlation with fetal lactate concentration. We conclude that the dilution in the fetal/maternal leucine- enrichment ratio correlates with the severity of growth restriction and reflects decreased transplacental leucine flux and/or increased protein breakdown within the fetoplacental compartments.