Impact of active phase duration on neonatal and maternal adverse outcomes: A systematic analysis of parity stratification, body mass index interaction, and predictive modeling in a retrospective cohort

Abstract Background A prolonged active phase of labor is associated with adverse maternal and neonatal outcomes, but its clinical significance in contemporary obstetric populations, including the unique Chinese demographic context, and its modification by parity and body mass index (BMI) remain incompletely defined. Methods A single‐center retrospective cohort study included 2873 women with term (≥37 weeks), singleton, cephalic vaginal deliveries. Active phase duration (defined as time from 5 cm to 10 cm cervical dilation) was categorized into short, medium, and prolonged groups (33rd/66th percentiles). Multivariable logistic regression and restricted cubic spline (RCS) analyses were used to adjust for confounders, test interactions, and explore nonlinear trends. Predictive models incorporating active phase duration, parity, and clinical covariates were validated using area under the receiver operating characteristic curve (AUC). Primary outcomes were composite neonatal morbidity and composite maternal morbidity. Secondary outcomes included individual neonatal (e.g., neonatal intensive care unit admission and fetal distress) and maternal (e.g., postpartum hemorrhage) outcomes. Results Among nulliparous women, prolonged active phase duration significantly increased risks of composite neonatal morbidity (adjusted odds ratio [aOR] 2.08, 95% confidence interval [CI] 1.23–3.52; P = 0.006), neonatal intensive care unit admission (aOR 1.97, 95% CI 1.06–3.67; P = 0.032), fetal distress (aOR 2.47, 95% CI 1.37–4.44; P = 0.003), postpartum hemorrhage (aOR 1.62, 95% CI 1.09–2.41; P = 0.018), and composite maternal morbidity (aOR 1.74, 95% CI 1.18–2.56; P = 0.005). No significant associations were observed in multiparous women. BMI modified these relationships ( P interaction