Establishment and validation of a clinical prediction model for predicting early postpartum pelvic floor muscle weakness among primiparous women after vaginal delivery: a retrospective study

Background Pelvic floor muscle weakness (PFMW) is a significant postpartum complication linked to pelvic floor dysfunction. PFMW impairs quality of life and requires early intervention. This study aimed to develop and validate a clinical prediction model for early postpartum PFMW in primiparous women after vaginal delivery. Methods This retrospective cohort study was conducted at a tertiary maternity hospital in Shanghai, China. Primiparous women with vaginal deliveries (July 2021–December 2023) were enrolled. Participants were assessed for PFMW using pelvic floor surface electromyography (sEMG) via the Glazer protocol at 42–90 days postpartum. Maternal and obstetric predictors were analyzed via univariable and multivariable logistic regression to construct a nomogram. Model performance was evaluated using concordance statistics (C-statistics), calibration curves, and decision curve analysis in both the training ( n = 2,465) and validation ( n = 1,049) cohorts. Internal validation was performed via ten-fold cross-validation. Results Among 3,514 enrolled women, PFMW occurred in 25.55% (898/3,514), with comparable baseline characteristics between cohorts (age, pre-pregnancy BMI; P > 0.05). Multivariable analysis revealed five independent predictors: maternal age (OR 1.156, 95% CI 1.116–1.999), gestational weight gain (OR 1.146, 95% CI 1.116–1.178), instrumental delivery (forceps: OR 1.904, 95% CI 1.336–2.714), prolonged second stage of labor (OR 1.026, 95% CI 1.022–1.029), and infant weight (OR 1.003, 95% CI 1.002–1.003). The nomogram demonstrated strong discrimination [C-statistic: 0.866 (95% CI 0.850–0.882) in the training cohort; 0.870 (0.819–0.903) in the validation cohort] and good calibration. Decision curve analysis confirmed the clinical utility across threshold probabilities (0–0.3). Conclusion This study established a validated nomogram integrating maternal and obstetric factors to predict early postpartum PFMW in primiparous women after vaginal delivery. This tool may aid in the early identification of high-risk individuals, enabling targeted rehabilitation to mitigate long-term pelvic floor dysfunction.