Evaluation of Neonatal Acute Hypoxia at Delivery Using Fetal Physiology and Eucapnic pH Assessment

Cardiotocography (CTG) is widely used for intrapartum fetal surveillance; however, traditional pattern-recognition approaches may not always reflect the underlying fetal physiological response to hypoxic stress. Recently, physiology-based CTG interpretation frameworks have been proposed to improve identification of fetal compensation and decompensation mechanisms during labor.

Similarly, conventional interpretation of umbilical cord blood gas analysis may not adequately distinguish respiratory from metabolic components of neonatal acidemia. Eucapnic pH, calculated by correcting for the respiratory component of acid-base imbalance, has been proposed as a tool to better characterize metabolic compromise at birth.

This ambispective observational study aims to re-evaluate CTG tracings obtained during labor using a physiology-based interpretative framework and to integrate these findings with arterial umbilical cord blood gas parameters, including measured pH, base excess, pCO2, and calculated eucapnic pH.

The study includes a retrospective cohort of term singleton deliveries and a prospective cohort of consecutively enrolled term pregnancies undergoing intrapartum CTG monitoring. CTG recordings will undergo blinded re-evaluation by independent reviewers using physiology-based criteria. These findings will be integrated with maternal, intrapartum, and neonatal variables to explore relationships between CTG characteristics, types of hypoxic exposure, acid-base status, and neonatal outcomes.

The study aims to determine whether physiology-based CTG interpretation identifies fetal compromise not recognized using conventional interpretation methods and to evaluate the relationship between CTG findings, eucapnic pH, and neonatal condition at birth. The results may contribute to improving understanding of intrapartum fetal adaptation and refining strategies for fetal surveillance during labor.