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BACKGROUND: It is well known that breastfeeding provides favorable health outcomes for both mother and baby. However, many mothers struggle to meet global recommendations to exclusively breastfeed for 6 months. Of those who cease breastfeeding early, one third attribute this to perceived insufficient milk supply. Currently, it is uncertain how the perception of insufficient milk supply relates to physiological milk volume or nutrient composition. OBJECTIVE: The Māmā and Baby Breastfeeding Study aims to estimate human milk volumes produced by a diverse sample of breastfeeding mothers at 3 months post partum with differing perceptions of milk supply and to investigate human milk composition in relation to milk volume. METHODS: We plan to recruit a sample of 150 mother-infant dyads in this observational study in Dunedin, Aotearoa New Zealand. Participants will represent a diverse range of ethnicities and socioeconomic backgrounds. Human milk volume will be assessed using the dose-to-mother stable isotope (deuterium oxide) technique. Mother participants will consume an accurate dose (30 g) of deuterium oxide after baseline saliva samples are collected from both mother and infant. Subsequent postdose samples will be collected over 3 time points to determine deuterium enrichment over a 14-day period using Fourier transform infrared spectrometry. Human milk macronutrient (energy, fat, carbohydrate, crude protein, and true protein) and mineral and trace element (sodium, magnesium, phosphorus, potassium, calcium, iron, copper, zinc, selenium, and iodine) composition of 1 full milk expression from 1 breast will be analyzed using the MIRIS Human Milk Analyzer (Miris AB) and inductively coupled plasma mass spectrometry, respectively. Potential predictors and maternal perception of milk supply will be assessed via questionnaire. Infant BMI will be calculated from measures of weight and length at 3 different time points over 4 weeks, using standard techniques. These, alongside anthropometric measurements collected at the infant's Well Child Tamariki Ora visits, will be used to assess infant growth trajectory in the first 6 months of life. Regression models will be used to assess the associations between maternal perception of milk supply, human milk volumes, and composition. RESULTS: This study was funded in April 2023 by the Health Research Council of New Zealand (grant 23/461). Recruitment for this study began in February 2025 and is anticipated to conclude in June 2026, with analysis expected to be completed by February 2027. As of January 17, 2026, a total of 91 participants have been enrolled. Final results are anticipated to be disseminated in late 2027 following completion of data analysis. CONCLUSIONS: This research will provide new knowledge on whether maternal perception of milk supply aligns with actual human milk volume or nutrient composition. Such information will be extremely useful for health professionals working with breastfeeding mothers with milk supply concerns and for informing the design of breastfeeding support programs and resources. TRIAL REGISTRATION: Australian and New Zealand Clinical Trial Registry ACTRN12625000180415; https://www.anzctr.org.au/ACTRN12625000180415.aspx. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/84776.
Bruckner et al. (Thu,) studied this question.