Clinical Significance of Severe and Borderline Umbilical Acidemia: Arterial pH, Lactate, Base Excess and Apgar Score Dynamics in Early Neonatal Risk Stratification

Background: While Apgar score is still the cornerstone of perinatal assessment, umbilical cord blood acid–base analysis provides objective information on fetal acid–base status at birth. Guidelines recommend cord blood gas evaluation in selected high-risk cases of low Apgar scores. However, newborns with severe and borderline acidemia may have temporarily reassuring Apgar scores despite biochemical evidence of metabolic stress. This study aimed to evaluate the clinical significance of severe and borderline umbilical acidemia, especially in the case of pH 7.19–7.10 values as a gray zone, and to assess whether lactate, base excess and metabolic burden score improve neonatal risk stratification. Methods: We performed a retrospective analysis of 1.989 newborns with available (routine) umbilical cord arterial blood gas parameters and 1 and 5 min Apgar scores. Severe and borderline acidemia were defined as arterial pH < 7.10 and 7.19–7.10, respectively. Arterial pH, lactate and base excess parameters were assessed, along with 1 and 5 min Apgar scores and early perinatal outcomes including the need for neonatal intensive care unit admission and CPAP requirement. Results: Close observation or NICU admission was associated with lower pH, higher lactate, and more negative base excess with a higher metabolic burden score. Among newborns with arterial pH < 7.20 (n = 299), ROC analysis showed lactate with the highest discriminative performance for close observation or NICU admission (AUC 0.783), followed by metabolic burden score (AUC 0.759). Both lactate and the metabolic burden score outperformed the pH risk alone. Although Apgar scores were statistically lower among admitted newborns, median 5 min Apgar values remained clinically reassuring. Conclusions: Severe and borderline umbilical arterial acidemia may identify neonates requiring closer observation. Integrating lactate, base excess, metabolic burden score and Apgar score dynamics may improve early risk stratification to discover perinatal hypoxia, with identification of newborns requiring close postnatal observation.