Why Emphasize Early Postpartum Pumping? The Critical Window for Coming to Volume in Pump-Dependent Mothers and Its Predictive Value for Feeding Method at Preterm Infants’ Discharge

Objectives: Mothers of preterm infants who experience mother–infant separation frequently face increased challenges with lactation. This study aims to analyze the critical window for coming to volume (CTV) and its associated risk factors in pump-dependent mothers and to investigate the predictive value of postpartum expressed milk volume for the feeding method at discharge in preterm infants. Study Design: A prospective observational study was conducted between July 2020 and February 2021. Lactation diaries kept by mothers of preterm infants admitted to a neonatal intensive care unit in Guangzhou, China, were collected during this period. Binary multivariable Logistic regression, time-series analysis, Spearman correlation analysis, and K-Prototype cluster analysis were employed to investigate the critical window for CTV and its risk factors. The area under the receiver operating characteristic curves were used to evaluate the ability of expressed milk volume during postpartum days 8–14 to predict the feeding method at discharge for preterm infants. Results: Data from 1,232 diary days completed by 88 mothers were analyzed. 51.14% of mothers of preterm infants failed to CTV. Unscheduled pumping, a lower average pumping frequency on postpartum day 1–7, a lower average expressed breast milk volume on postpartum day 1–7, and a small intra-session bilateral volume discrepancy were identified as independent risk factors for no-CTV. During postpartum days 3–7, both pumping frequency and milk volume increased progressively. The frequency and volume of pumping between postpartum days 3 and 7 positively correlated with the milk volume on postpartum day 14. Clustering analysis based on early postpartum pumping behaviors identified two groups: High-Frequency Timed Group (HFTG) and Low-Frequency Untimed Group. The HFTG exhibited higher pumping frequency and milk volume, indicating a greater likelihood of achieving CTV. The expressed breast milk volume on postpartum day 8 significantly predicted the feeding method at discharge (Area Under the ROC Curve [AUC] [95% confidence interval]: 0.831 [0.746–0.916]), with no statistically significant difference in predictive performance compared to volumes on days 9–14 ( p > 0.05). Conclusion: Postpartum days 3–7 represent the critical window for CTV among mothers of preterm infants, during which pumping behavior directly influences CTV. Postpartum day 8, as the first day following the critical window, provides an early and effective prediction of feeding outcomes at discharge.