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

OBJECTIVE: We have previously demonstrated an increase in the glycine/valine ratio (G/V) in anmiotic fluid (AF) from fetuses with intrauterine growth restriction (IL'GR) consistent with a pattern of chronic starvation. We hypothesized an association of elevated AF G/V and neonatal morbidity in IUGR newborns. STUDY DESIGN: AF's were obtained from 122 third trimester pregnancies (range 31-39 weeks). Forty nine pregnancies were complicated by IUGR. Amino acid analysis was performed by high pressure liquid chromotography. G/V's were compared between normal and IUGR fetuses. Neonatal morbidity within the group of IUGR fetuses was characterized by evaluation of neonatal hypoglycemia, arterial cord blood gas analysis, and birth weight percentile (BW%). We also examined the correlation of AF G/V to the umbilical artery resistance index. The mean (s.d.) interval between AF sampling and delivery was 3.5 days (4.8). Analysis was performed by Student's t-test or simple correlation (p < 0.05 accepted for significance). RESULTS: IUGR fetuses have a significantly elevated AF G/V compared to control subjects (IUGR: 3.31 (1.06), C: 2.61 (0.77) p < 0.001). There was no dependence of G/V on gestational age for either group. An elevated G/V ratio was not associated with neonatal hypoglycemia (HYPO) within the IUGR group (HYPO: (n = 16) 3.19 (1.07), No HYPO (n = 30) 3.44 ( 1.09) p = NS). There were no significant correlations of G/V with arterial cord blood pH, p()2, or base deficit; (G/V v. pH: r = -0.10, G/V v. PO2: r = 0.04, G/V v. base deficit: r = 0.12, all p = NS). There was no significant correlation of G/V with BW% (r = -.24, p = 0.10) or umbilical artery Rl (r = -0.14). CONCLUSION: AF G/V ratios are elevated in IUGR fetuses compared to control fetuses. However, contrary to our hypothesis the level of G/V is not associated with neonatal morbidity as evidenced by hypoglycemia, arterial cord blood gas abnormalities or BW%.