Amniotic fluid glycine/valine ratio and neonatal morbidity in fetal growth restriction

Objective: To test the hypothesis that an elevated amniotic fluid glycine-valine ratio predicts neonatal morbidity in growth-restricted newborns. Methods: Amniotic 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 Student t test, χ2 with Yates correction, or simple correlation when appropriate. P < .05 was considered significant. Results: Growth-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 glycine-valine 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 ratio and birth weight percentile (r = −.24) or umbilical artery resistance index (r = −.14). Conclusion: Amniotic fluid glycine-valine ratio is elevated in growth-restricted fetuses compared with control fetuses. However, the level of glycine-valine elevation is not associated with neonatal morbidity related to hypoglycemia, arterial cord blood gas abnormalities, or birth weight percentile.