Early Postpartum Milk-Expression and Expressed-Milk Feeding Practices in Relation to Breastfeeding Outcomes: A Systematic Review.

Background/Objectives: Early postpartum milk expression is common, but its relationship with later breastfeeding outcomes depends on the clinical context in which expression is used. This systematic review examined distinct exposure domains, including expression method, timing and intensity of expression, expressed-milk feeding modality, composite in-hospital feeding patterns, and clinically indicated expression in pump-dependent populations. Methods: Following PRISMA 2020 guidance, primary studies of postpartum milk expression, breast pump use, or expressed breast-milk feeding were identified and synthesized using a PECO framework. Because included studies differed substantially in population, exposure definition, comparator structure, and outcome measurement, meta-analysis was not undertaken. Instead, studies were grouped a priori into exposure families, and conclusions were derived within each domain while explicitly considering risk of bias was assessed using RoB 2, version of 22 August 2019, for randomized trials and the original 2016 version of ROBINS-I for non-randomized studies. Results: Seventeen studies met the eligibility criteria. In healthy term dyads, routine early pumping or exclusive/predominant expressed-milk feeding was generally associated with less favorable breastfeeding continuation than direct feeding at the breast, although these associations were mainly derived from observational studies at serious risk of confounding by indication. In preterm, separated, or otherwise pump-dependent dyads, earlier and more frequent milk expression was associated with improved early lactation outcomes, including lactogenesis, milk yield, or achievement of full lactation; evidence for longer-term breastfeeding continuation was more limited. Broad population-level definitions of any pump use produced less consistent findings and were not directly comparable with studies of exclusive expressed-milk feeding. Conclusions: Early postpartum milk expression should be interpreted as a context-dependent practice rather than as a uniform exposure. The strongest clinical inference is that direct breastfeeding should be supported when feasible in healthy term dyads, whereas early and frequent expression remains necessary and potentially beneficial when direct breastfeeding is not immediately possible.