Maternal Perception vs Actual Breast Milk Supply: Is There a Difference? Protocol for the MABBS Observational Study (Preprint)

<sec> <title>BACKGROUND</title> It is well known that breastfeeding provides favourable health outcomes for both mother and baby. However, many mothers struggle to meet global breastfeeding recommendations, with Perceived Insufficient Milk Supply (PIMS) being a leading reason for early cessation. Currently, little is known about the relationship between PIMS, actual milk insufficiency, and human milk nutrient composition. </sec> <sec> <title>OBJECTIVE</title> The main aims of the Māmā (mother) and Baby Breastfeeding Study (MABBS) are to estimate human milk volumes produced by a diverse sample of breastfeeding mothers at 3 months postpartum with differing perceptions of milk supply, and to investigate human milk composition in relation to milk volume. </sec> <sec> <title>METHODS</title> In this observational study in Dunedin, Aotearoa New Zealand, a sample of 150 mother-infant dyads will be recruited. A diverse range of participants in terms of ethnicity and socio-economic status will be included. 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 post-dose 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 and true protein) and mineral and trace element (sodium, magnesium, phosphorus, potassium, calcium, iron, copper, zinc, selenium, iodine) composition of one full milk expression from one breast will be analyzed using the MIRIS Human Milk Analyzer and ICP-MS, respectively. Potential predictors and maternal perception of milk supply will be assessed via questionnaire. Infant body mass index (BMI) will be calculated from measures of weight and length at three different time points over four 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 six months of life. Regression models will be used to assess the associations between maternal perception of milk supply, human milk volumes, and composition. </sec> <sec> <title>RESULTS</title> 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 the 25th of September 2025, 64 participants have been enrolled. </sec> <sec> <title>CONCLUSIONS</title> 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 programmes and resources. </sec> <sec> <title>CLINICALTRIAL</title> Australian and New Zealand Clinical Trial Registry ACTRN12625000180415; https://www.anzctr.org.au/ACTRN12625000180415.aspx </sec>