Breastfeeding is beneficial to the health of both the mother and infant. Despite recommendations to breastfeed by organisations including the WHO and the American Academy of Pediatrics, rates of breastfeeding remain below public health goals. The Mother and Infant Metabolome and Microbiome (MIMM) study is a prospective cohort study of healthy mother-term infant dyads designed to comprehensively assess the perinatal, maternal, neonatal and infant factors that are associated with breastfeeding outcomes and human milk composition.

MIMM participants were recruited from two medical centres in Boston, Massachusetts, from 2019 to 2023 and are followed for 2 years. Dyads were included if the mother delivered a singleton infant at ≥37 weeks’ gestation, was discharged home 2 and infant gestational age was 39.3 weeks. Approximately 43% of infants were born via caesarean delivery, and 45.5% were female.

MIMM study procedures include longitudinal (1) collections of maternal blood, vaginal swab, stool and milk and infant blood and stool samples and (2) assessments of breastfeeding status, child neurodevelopment and growth and maternal health at birth, 6 weeks and 6, 12, 18 and 24 months. Data collection through 18 months is complete. The overall objective of the MIMM study is to identify potential targets to improve breastfeeding outcomes, human milk composition and ultimately, maternal and child health. Preliminary analyses, reported in conference presentations (with ongoing analyses and results manuscripts pending), have found that (1) mothers with higher levels of stress were less likely to be exclusively breastfeeding their infants at 6 weeks; (2) higher breastfeeding intensity was associated with greater postpartum weight loss at 6 weeks; (3) feeding type was a more relevant predictor of feeding frequency and volume compared with feeding mode; (4) infants who received exclusive human milk had higher food enjoyment compared with those who received any formula; and (5) infants of mothers with obesity had higher average feeding volume per feed.

Data collection for the final 24-month visit is expected to be completed by August 2025. We expect that all sample assays will be completed by December 2025. Findings will continue to be submitted for presentation at scientific conferences, and we expect to publish the first findings from this cohort in manuscript format in 2025.