Utility of Admission and Intrapartum Cardiotocography for Predicting Umbilical Artery pH Status at Birth: A Retrospective Cohort Study in Iran

Abstract

Background and Aims: Intrapartum cardiotocography (CTG) is used to detect fetal hypoxia, but static classifications can miss progressive compromise. This study analyzes longitudinal CTG trends to find early predictors of umbilical artery acidemia (pH < 7.20) at birth. Methods: A retrospective cohort study analyzed vaginal deliveries (2019-2022) at a tertiary hospital. Singleton pregnancies were stratified into cases (pH < 7.2, n = 70) and controls (pH >= 7.2, n = 182). CTG tracings were assessed for baseline FHR, beat-to-beat variability (BTBV), accelerations, and decelerations at four timepoints: admission, latent and active first-stage labor, and second-stage labor. Univariate and multivariate logistic regression (adjusted for maternal age, comorbidities, and gestational age) identified predictors, with receiving operating characteristic (ROC) analysis evaluating predictive performance. Results: We found that neonatal acidemia at birth was predicted by elevated baseline FHR at admission, contrasted with decreased FHR during active first-stage and second-stage labor. Progressive reduction in BTBV showed a strong association at all stages of labor, most prominent at second-stage labor, absent accelerations during first-stage labor, and presence of decelerations, especially late decelerations during second-stage labor. ROC analysis demonstrated excellent predictive performance for second-stage BTBV (AUC = 0.992) and baseline FHR (AUC = 0.914). Conclusion: Specific evolving CTG patterns effectively predicted fetal acidemia. Parameters from the second stage of labor were most predictive, underscoring the critical importance of continuous monitoring to identify high-risk cases and guide timely intervention for fetal hypoxia.