BACKGROUND Umbilical artery gas results help obstetricians to assess fetal well being during the course of labor and guide screening decisions on eligibility for therapeutic hypothermia or also know as whole body or head cooling. The accuracy of results, especially base deficit on arterial cord gas analysis, in predicting brain injury is questioned. A novel biomarker specifically calculated for fetal acid-base physiology and response to asphyxia-neonatal eucapnic pH as a marker of neonatal metabolic acidosis-has the potential to be an accurate predictor of hypoxic-ischemic encephalopathy. OBJECTIVE We aimed to compare false-negative rates of hypoxic-ischemic encephalopathy for umbilical artery pH, base deficit, and neonatal eucapnic pH in assessing fetal acid-base balance as a marker of fetal well being and predicting acute brain injury. METHODS This is a retrospective single-center cohort study of newborns ≥ 35 weeks' gestation diagnosed with hypoxic-ischemic encephalopathy. We compared false-negative rates for any grade of hypoxic-ischemic encephalopathy using unilateral paired χ2 statistical analysis based on cut-off values for umbilical artery pH ≤ 7.00, base deficit ≥ 16 mmol/L, base deficit ≥ 12 mmol/L and neonatal eucapnic pH ≤ 7.14. We performed analysis of variance between umbilical artery pH, base deficit, and neonatal eucapnic pH for each hypoxic-ischemic encephalopathy grade. RESULTS We included 113 newborns. False-negative rate for hypoxic-ischemic encephalopathy was significantly higher for base deficit < 16 mmol/ (n=78/113; 69.0%) compared to base deficit < 12 mmol/L (n=46/113; 40.7%), pH > 7.00 (n=41/113; 36.3%) or neonatal eucpanic pH > 7.14 (n=35/113; 31.0%) (p<0.0001). All true positive cases were identified using only umbilical artery pH and neonatal eucapnic pH. Base deficit ≥16 or ≥12 mmol/L did not add any value in identifying newborns with hypoxic-ischemic encephalopathy when using umbilical artery pH and neonatal eucapnic pH. No association emerged between any marker and hypoxic-ischemic encephalopathy severity grading. CONCLUSIONS Our findings support the accuracy of neonatal eucapnic pH to assess fetal well being during labor and to improve predictive performance for acute brain injury. Neonatal eucpanic pH, in addition to umbilical artery pH, may be a viable alternative in identifying newborns at risk for hypoxic-ischemic encephalopathy.