Why do mothers mix milk feed their infants? Results from a systematic review.

CONTEXT: Combining or supplementing breastfeeding with formula feeding, also called mixed milk feeding (MMF), is a common infant feeding practice. However, there is no well-established MMF evidence-base for informing and guiding parents. A better understanding of the reasons why mothers practice MMF may facilitate identification of efficient strategies for supporting exclusive breastfeeding, and/or opportunities to prolong breastfeeding, at least partially. OBJECTIVE: An updated systematic literature review was undertaken with the primary aim of gaining a deeper understanding of the reasons why mothers choose MMF. DATA SOURCES: Six databases were searched for relevant articles published in English from January 2012 to January 2022. DATA EXTRACTION: Two reviewers independently performed the screenings and data extraction, and any differences were resolved by a third reviewer. Data from 138 articles were included, 90 of which contained data on MMF reasons/drivers, and 60 contained data on infant age and/or maternal demographic factors associated with MMF. DATA ANALYSIS: A total of 13 different unique MMF drivers/reasons were identified and categorized according to whether the drivers/reasons related to perceived choice, necessity, or pressure. Risk of bias was evaluated using the Quality Assessment Tool of Diverse Studies and the JBI Systematic Reviews tool. Several different terms were used to describe and classify MMF across the studies. The most commonly reported reasons for MMF were related to a perception of necessity (39% of drivers, eg, concerns about infant's hunger/perceived breast milk insufficiency or breastfeeding difficulties), followed by drivers associated with perceived choice (34%; eg, having more flexibility) and perceived pressure (25%; eg, returning to work or healthcare professionals' advice). This was particularly true for infants aged 3 months or younger. CONCLUSION: The key global drivers for MMF and their distribution across infant age and regions were identified and described, providing opportunities for the provision of optimal breastfeeding support. A unified definition of MMF is needed in order to enable more comparable and standardized research. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration no. CRD42022304253.

Mixed milk feeding: a systematic review and meta-analysis of its prevalence and drivers.

CONTEXT: Extensive literature is available on exclusive breastfeeding and formula-feeding practices and health effects. In contrast, limited and unstructured literature exists on mixed milk feeding (MMF), here defined as the combination of breastfeeding and formula feeding during the same period in term infants > 72 hours old (inclusion criterion). OBJECTIVE: A systematic review and meta-analysis were performed, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, on the global prevalence of MMF (primary outcome) and related drivers and practices (secondary outcomes). DATA SOURCES: The search of MMF in generally healthy populations was conducted across 6 databases, restricted to publications from January 2000 to August 2018 in English, Spanish, French, and Mandarin. DATA EXTRACTION: Two reviewers independently performed screenings and data extraction according to a priori inclusion and exclusion criteria. DATA ANALYSIS: Of the 2931 abstracts identified, 151 full-text publications were included for data extraction and 96 of those were included for data synthesis (the majority of those were cross-sectional and cohort studies). The authors summarized data across 5 different categories (feeding intention prenatally, and 4 age intervals between > 72 hours and > 6-23 months) and 5 regional subgroups. The overall prevalence of MMF across different age intervals and regions varied between 23% and 32%; the highest rate was found for the age group 4-6 months (32%; 95% confidence interval, 27%-38%); regional comparisons indicated highest MMF rates in Asia (34%), North and South America (33%), and Middle East and Africa together (36%), using a random effects meta-analysis model for proportions. Some drivers and practices for MMF were identified. CONCLUSION: MMF is a widespread feeding reality. A shared and aligned definition of MMF will help shed light on this feeding practice and evaluate its influence on the duration of total breastfeeding, as well as on infants' nutrition status, growth, development, and health status in the short and long terms. PROSPERO registration number CRD42018105337.