Factors influencing delayed lactogenesis II among advanced-age women following cesarean section: a retrospective analysis and predictive model development.

Background: Delayed lactogenesis II (DLII), defined as the onset of copious milk secretion after 72 h postpartum, is a common complication that may impair early breastfeeding success. Advanced maternal age and cesarean delivery are both known risk factors, yet few studies have developed predictive models to identify high-risk women. This study aimed to construct and internally validate a clinical prediction model for DLII among advanced-age women undergoing cesarean section. Methods: This retrospective observational study analyzed the medical records of 325 women aged ≥35 years who underwent cesarean delivery at a tertiary maternal and child health hospital in Southwest China between January 2021 and January 2025. Maternal, obstetric, surgical, and neonatal variables were extracted from electronic medical records. Univariate and multivariate logistic regression analyses were performed to identify independent predictors of DLII, and a nomogram was subsequently developed. Model discrimination and calibration were assessed using the area under the receiver operating characteristic (ROC) curve (AUC), Hosmer-Lemeshow goodness-of-fit test, and calibration plots with 1,000 bootstrap resamples. Results: Of the 325 women included, 117 (36.0%) experienced DLII. Multivariate analysis identified maternal age (aOR = 1.15, 95% CI 1.01-1.32), pre-pregnancy body mass index (BMI; aOR = 1.10, 95% CI 1.00-1.22), primiparity (aOR = 1.74, 95% CI 1.02-2.96), and shorter gestational age (aOR = 0.71, 95% CI 0.55-0.91) as independent risk factors for DLII. In contrast, elective cesarean section and early postpartum practices (rooming-in within 24 h, breastfeeding initiation within 24 h, and early skin-to-skin contact) were associated with lower odds of delayed lactogenesis II after multivariable adjustment (all Conclusion: This study established a reliable and clinically interpretable model for predicting delayed lactogenesis II among advanced-age women undergoing cesarean section. The model showed high accuracy and good internal validity, highlighting the relevance of maternal characteristics and early postpartum behaviors to lactation outcomes. The proposed nomogram may serve as a practical tool for early risk identification and targeted breastfeeding support in clinical settings.