Umbilical artery eucapnic pH to assess fetal well-being.

Background: Umbilical artery gas results help obstetricians assess fetal well-being during labor and guide screening decisions on eligibility for therapeutic hypothermia (ie, whole-body or head cooling). The accuracy of results, especially for the 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.

Study Design: This is a retrospective single-center cohort study of newborns ≥ 35 weeks of gestation diagnosed with hypoxic-ischemic encephalopathy. We compared false-negative rates for any grade of hypoxic-ischemic encephalopathy using unilateral paired chi-square statistical analysis based on cutoff 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 an 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/L (n=78/113; 69.0%) than <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<.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.

Conclusion: 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.