Prediction of the second stage of labor duration using prelabor ultrasound markers

초록

Objectives: To determine whether prelabor intrapartum ultrasound predicts a short second stage of labor (≤1 hour). Methods: We conducted a single-center observational cohort of 86 vaginal delivery recruited from January 2022 to August 2025 and stratified participants by second-stage duration (≤1 h, n = 34; >1 h, n = 52). Baseline maternal characteristics and delivery outcomes were recorded, and prelabor ultrasound was used to quantify cervical configuration and fetal head descent. Multivariable logistic regression (adjusted for age and BMI) evaluated predictors of a ≤1 h second stage. Discrimination was quantified by ROC (Receiver Operating Characteristic) analysis; Pearson’s correlation tested associations with birth weight. Results: Most baseline characteristics did not differ by group. Oxytocin use and epidural use trended higher with >1 h. Operative delivery was markedly more frequent with >1 h (47.1% vs 11.4%, p=0.001). Among ultrasound markers, only anterior cervical angle (ACA) differed significantly (121.7◦ ±18.2 vs 109.5◦ ±23.2, p=0.025); Progression distance(PD), angle of progression (AoP), head–perineum distance (HPD), head–symphysis distance (HSD), cervical length(CL), and posterior cervical angle (PCA) were non-significant (all p>0.05). In multivariable analysis, ACA independently predicted a ≤1 h second stage (adjusted OR 1.028 per degree, 95% CI 1.002–1.058, p=0.045); age and BMI were not significant. The ROC curve AUC for ACA was 0.651 (95% CI 0.515–0.787; p=0.04). A cut-off of 107.3◦ yielded 82.8% sensitivity and 50% specificity. Conclusions: A wider ACA measured before labor is an independent predictor of a short second stage (≤1 h). Mechanistically, this association may reflect an axis-alignment effect where a more anteriorly open cervix better aligns with the direction of expulsive forces, facilitating fetal descent.