Maternal and infant microbiota in early infancy: Longitudinal findings from a randomised controlled trial

Objectives To characterise early postnatal microbial development across maternal gut, breast milk, and infant gut compartments, and explore potential modulation by maternal stress in a cohort of Chinese mothers practising traditional postpartum confinement. Methods This secondary analysis draws on a randomised controlled trial of a maternal relaxation intervention in late preterm and early‐term dyads. Vaginally delivered mothers (34 + 0 to 37 + 6 weeks) and their exclusively breastfed infants were followed from 1 to 8 weeks postpartum. Maternal stool, breast milk, and infant stool samples were collected at both time points and analysed via 16S rRNA gene amplicon sequencing. Changes in gut microbiome diversity and composition (alpha andbeta diversity metrics) and the relative abundance of dominant genera were assessed overall and by intervention group. Results Microbiome diversity (alpha diversity metrics) remained stable across all sample types. However, we observed a compositional temporal shift in breast milk microbiota ( p = 0.039), driven primarily by changes in the control group. Infant gut microbiota showed increased Bifidobacterium and decreased Staphylococcus and Enterobacteriaceae with time. A significant reduction in Staphylococcus was observed in breast milk of the intervention group only. Maternal gut microbiota remained stable. Conclusions Microbial composition in breast milk and infant gut shifted over the first 8 weeks postpartum, while maternal gut remained stable. Findings suggest maternal stress‐reduction interventions may influence breast milk microbiota. Further research is warranted to confirm these effects and investigate mechanisms.