The Expanded Biopsychosocial Model Elucidates the Association Between Pre-Pregnancy Overweight/Obesity and Delayed Lactogenesis II: A Prospective Cohort Study.

Pre-pregnancy overweight or obesity delays the onset of lactogenesis II, posing an early barrier to achieving optimal infant nutrition and long-term health. However, the underlying pathophysiological mechanisms remain incompletely elucidated. This prospective cohort study conducted in China aimed to delineate the distinct pathways through which pre-pregnancy overweight/obesity, compared to normal body mass index (BMI), leads to delayed lactogenesis II. Guided by an expanded biopsychosocial framework, we enrolled and stratified 296 primiparous women into pre-pregnancy overweight/obese (n = 146) and normal BMI (n = 150) groups. Data on biological, psychological, social, and infant-related factors were collected prospectively at prenatal, delivery, and one-week postpartum stages. Structural equation modeling was used to identify and compare the mediating pathways between the two groups. Results demonstrated that the association between pre-pregnancy overweight/obesity and delayed lactogenesis II was primarily mediated through four distinct pathways: biological (e.g., breastfeeding difficulties: β = 0.203, 95% CI: 0.144-0.265, p < 0.001), psychological (e.g., internalized weight stigma: β = 0.095, 95% CI: 0.016-0.181, p = 0.026), social (e.g., reduced pro-breastfeeding practices: β = 0.076, 95% CI: 0.017-0.144, p = 0.019), and infant-related (e.g., higher formula intake: β = 0.114, 95% CI: 0.047-0.195, p = 0.003). This study validates the expanded biopsychosocial model by elucidating the distinct pathways through which pre-pregnancy overweight/obesity contributes to delayed lactogenesis II. These findings underscore the necessity for clinical practice to move beyond a purely biological focus and advocate for a paradigm shift in clinical support towards integrated, multi-faceted interventions tailored to this vulnerable population. TRIAL REGISTRATION: This study was registered at the Chinese Clinical Trial Registry (registry number: ChiCTR2200057038). The trial was registered on February 26, 2022.