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

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.

An updated systematic literature review was undertaken with the primary aim of gaining a deeper understanding of the reasons why mothers choose MMF.

Six databases were searched for relevant articles published in English from January 2012 to January 2022.

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.

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.

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.

PROSPERO registration no. CRD42022304253.