The Impact of Prolonged Deceleration During the Second Stage of Labor on Umbilical Artery Blood Gas Analysis

Objective: To investigate the association between prolonged deceleration during the second stage of labor and umbilical artery acid-base status. Methods: This retrospective study analyzed 122 singleton deliveries at Second Nanning People’s Hospital (2022– 2024). Participants were stratified into low pH (umbilical artery pH < 7.20, n=64) and normal pH (pH ≥ 7.20, n=58) groups. Variables included demographics, labor characteristics (delivery mode, deceleration-to-delivery interval), fetal heart rate (FHR) parameters (prolonged deceleration duration, FHR nadir, non-periodic accelerations, baseline variability), complications, and neonatal outcomes. Results: The low pH group exhibited longer prolonged deceleration periods (p< 0.05), greater FHR declines (p< 0.05), and fewer non-periodic accelerations (p< 0.05). Multivariate analysis identified prolonged deceleration duration and FHR decline magnitude as independent predictors of low pH. No significant intergroup differences existed in maternal BMI, gestational age, or delivery mode. Conclusion: Our findings indicate that prolonged deceleration and fetal heart rate decrease are risk factors for low pH, underscoring the critical pH threshold of 7.2, below which the risk of neonatal asphyxia increases. These results highlight the importance of timely intervention during prolonged deceleration in labor to reduce adverse outcomes. Keywords: second stage of labor, prolonged deceleration, blood gas analysis