Maternal perception vs actual breast milk supply: is there a difference?

Saliva samples will be collected from mothers and infants at the first appointment, before administration of 30g of the stable isotope (deuterium oxide) (as a drink) to the mother by a trained researcher. Saliva samples will be taken from the mother and baby at the second visit (2 days post dose), third visit (7 days post dose) and fourth visit (14 days post dose) to measure the disappearance of deuterium from the mother and appearance in the infant (i.e. via the mothers breast milk). We will also ask mothers to collect an at home saliva sample on themselves (not the infant) 3-5 hours after stable isotope administration for body composition calculations. Infant weight and length will be taken at the first, fourth and fifth visit. Maternal weight and height will be taken at the first appointment. Data will be collected on demographics, maternal perception of breast milk supply, breastfeeding self-efficacy, infant sleep, as well as maternal stress and sleep, maternal health history (including eating patterns), and family factors (e.g., childcare attendance). The mother will be asked to pump a full breast milk expression and provide us with a 12ml sample as soon as possible after the fourth visit, for breast milk nutrient composition analysis. Visits one to four will be conducted by a trained researcher. A breastfeeding observation and oral assessment will be conducted at the fifth visit (approximately two weeks after the fourth visit) by an International Board Certified Lactation Consultant (IBCLC) to: a) observe for correct latch and positioning, as well as active and nonnutritive feeding, b) perform an oral assessment on the baby to identify any oral anomalies that could be causing transfer of breast milk issues, and c) perform a test-weight to get a one off estimate of milk transfer. Any latch/transfer issues observed during the feeding or discovered by the questionnaire will be noted by the Lactation Consultant. The mother will be asked questions on usual feeding and latching. With the mothers' permission, any appropriate referrals will be made (e.g., GP, specialist) and/or support provided by the Lactation Consultant for any concerns that may have arisen during the assessment. A final short (three question) survey will be sent to participants at the end of the study to assess how they felt after discussing breastfeeding with the Lactation Consultant. In total, participants will be asked to attend five visits over 4 weeks.