ObjectiveTo test the hypothesis that an elevated amniotic fluid glycine-valine ratio predicts neonatal morbidity in growth-restricted newborns.MethodsAmniotic fluid (AF) was collected from 122 third-trimester pregnancies (range 31–39 weeks), 49 of which were complicated by fetal growth restriction. Amino acid analysis was performed by high-pressure liquid chromatography. Glycine-valine ratios were compared between normal and growth-restricted fetuses. Neonatal morbidity within the group of growth-restricted fetuses was characterized by evaluation of neonatal hypoglycemia, arterial cord blood gas analysis, and birth weight percentile. We also examined the correlation of AF glycine-valine ratio to the umbilical artery resistance index. The median interval between AF sampling and delivery was 1 day (range 0–8 days). Analyses were performed by StudentttestX2with Yates correction, or simple correlation when appropriate.P< .05 was considered significant.ResultsGrowth-restricted fetuses have a significantly elevated AF glycine-valine ratio compared with control subjects (3.31 ± 1.06 versus 2.61 ± 0.77, respectively,P< .001). There was no association of the glycine-valine ratio with gestational age for either group. An elevated glycinevaline ratio was not associated with neonatal hypoglycemia within the growth-restricted group (hypoglycemia: [n= 16] 3.19 ± 1.07; no hypoglycemia; (n= 30) 3.44 ± 1.09). There were no significant correlations of glycine-valine ratio with arterial cord blood pH (r= −0.10), oxygen pressure (r= 0.04), or base deficit (r= 0.12). There were no significant correlations of glycine-valine ration and birth weight percentile (r= −.24) or umbilical artery resistance index (r= −.14).ConclusionAmniotic fluid glycine-valine ratio is elevated in growth restricted compared with control fetuses. However, he level of glycine-valine elevation is not associated with neonatal morbidity related to hypoglycemia, arterial cord blood gas abormalities, or birth weight percentile.