Utility of the capability, opportunity, and motivation behaviour (COM-B) model in explaining the negative association between pre-pregnancy body mass index and exclusive breastfeeding at six weeks postpartum

The mechanisms underlying the negative associations between pre-pregnancy body mass index (BMI) and exclusive breastfeeding remain poorly understood. Thus, the study aimed to determine whether the negative associations between high pre-pregnancy BMI and exclusive breastfeeding at six weeks postpartum are mediated by components of the capability, opportunity, and motivation behaviour (COM-B) model. In this prospective observational study, we assigned 360 primiparous women to a pre-pregnancy overweight/obese group (n = 180) and a normal-BMI group (n = 180). A structural equation model was designed to study how capabilities (onset of lactogenesis II, perceived milk supply, breastfeeding knowledge, and postpartum depression), opportunities (probreastfeeding hospital practices, social influence, social support), and motivations (breastfeeding intention, breastfeeding self-efficacy, and attitudes towards breastfeeding) affected exclusive breastfeeding at six weeks postpartum in groups of women with different pre-pregnancy BMIs. In all, 342 participants (95.0%) possessed complete data. Women with high pre-pregnancy BMI were less likely to exclusively breastfeed at six weeks postpartum than women with a normal BMI were. We observed a significant negative direct effect of high prepregnancy BMI on exclusive breastfeeding at six weeks postpartum and a significantly negative indirect effect of high pre-pregnancy BMI via the explanatory mediating variables of capabilities (onset of lactogenesis II, perceived milk supply, and breastfeeding knowledge) and motivations (breastfeeding self-efficacy) on exclusive breastfeeding at six weeks postpartum. Our findings support certain capabilities (onset of lactogenesis II, perceived milk supply, and breastfeeding knowledge) and motivations (breastfeeding self-efficacy), partially explaining the negative association between high pre-pregnancy BMI and exclusive breastfeeding outcome. We suggest that interventions aimed at promoting exclusive breastfeeding among women with high pre-pregnancy BMI should address the capacity and motivation factors specific to this population.