Development and Internal Validation of a Predictive Model for Prolonged Second-Stage Labor Using First-Stage Data: A...

Prolongation of the second stage of labor is associated with adverse maternal and neonatal outcomes, making early risk identification clinically important. This study assessed whether combining transabdominal and transperineal ultrasound parameters obtained during the first stage of labor could predict a prolonged second stage. This prospective observational study enrolled primiparas who underwent transabdominal and transperineal ultrasound during the active first stage of labor. Fetal position, angle of progression (AOP), head-pubic symphysis distance, head-perineum distance, and maternal clinical characteristics were recorded. Participants were classified into normal (≤120 min) and prolonged (>120 minutes) second-stage groups. Least absolute shrinkage and selection operator (LASSO) regression was used to select key predictors, and multivariable logistic regression identified independent predictors for model development. Predictive performance was evaluated using receiver operating characteristic (ROC) curve analysis, calibration, and decision curve analysis (DCA) during internal validation. The analysis included 159 primiparas (95 normal and 64 prolonged). Compared with the normal group, the prolonged group had higher incidences of fetal distress (31.2% vs 15.8%, p = 0.035) and low Appearance, Pulse, Grimace, Activity, and Respiration (Apgar) scores (70.3% vs 36.8%, p < 0.001). LASSO regression identified four key predictors-maternal age, gestational body mass index increase, neonatal birth weight, and AOP-all of which remained independent predictors (p < 0.05). The predictive model achieved an area under the ROC curve of 0.927 and demonstrated good discrimination, calibration, and clinical utility in internal validation. First-stage ultrasound parameters combined with maternal clinical characteristics may facilitate the early identification of high-risk primiparas and support intrapartum management.