Reliability and validity of the Spanish version of the Breastfeeding Motivation Scale (BMS). An approach to maternal mental health through psychological factors

Background: The decision to breastfeed can be complex due to the significant benefits of breastfeeding and the various barriers that mothers have to face. In this context, it is important to have adequate instruments that provide insight into a mother's motives for breastfeeding. Aim: Given the absence of instruments in this language, this study focuses on translating and validating the Breastfeeding Motivation Scale (BMS) in Spanish mothers. Method: After cultural adaptation and an item clarity assessment with a pilot sample (n = 28), exploratory factor analysis was conducted with a preliminary sample (n = 118). The main study involved 193 Spanish primiparous mothers, aged 24-48 (M = 34.5; SD = 4.2), recruited within two months postpartum, where confirmatory factor analysis, internal consistency, group comparisons, and validity measures were explored. Results: The findings (χ²=358.925, df=183, p<0.001, CFI=0.971, TLI=0.967, SRMR=0.079, and RMSEA=0.071 [90% CI: 0.060-0.081]) supported the existence of four motivational factors for breastfeeding: i) external and identified, ii) intrinsic, iii) integrated, and iv) introjected motivation. The four factors of the scale showed excellent internal consistency (ω_o ranging from 0.77 to 0.92), as well as good convergent and discriminant validity regarding theoretically-related variables (breastfeeding self-efficacy, positive attitude towards breastfeeding, and postpartum depression). Additionally, the scale showed incremental validity with respect to breastfeeding self-efficacy, but not regarding postpartum depression. Discussion: The BMS evidenced good psychometric properties in Spanish primiparous mothers. The findings are discussed in the context of Ryan and Deci's self-determination theory, also reviewing the study's limitations and implications.