Table 1.

Overview of participant contacts.

Study stage	Procedures
Recruitment: infants aged 0-2 months	Recruitment of potential participants
Screening: infants aged 6 weeks to 2 months	Eligibility questionnaire
Visit 1 (baseline): infants aged 2 to <4 months	Written consent Baseline saliva samples (mother and infant) Isotope administration (mother only) Anthropometry (mother and infant) Main questionnaire Note: the mother is asked to collect a saliva sample (mother only) 3-4 hours after the dose is administered
Visit 2: 2-3 days after baseline	Follow-up (postdose) saliva samples (mother and infant) Collect postdose saliva sample, that was self-collected by the mother after visit 1 (mother only)
Visit 3: 6-7 days after baseline	Follow-up (postdose) saliva samples (mother and infant)
Visit 4: 13-14 days after baseline	Final (postdose) saliva samples (mother and infant) Anthropometry (infant only)
Human milk collection: approximately 3 days after visit 4	Collection of 12 mL subsample of full milk expression from single breast
Visit 5: 2 weeks after visit 4	Anthropometry (infant only) Single test-weigh = weight before and after a breastfeed (infant) Breastfeeding assessment Oral assessment D-MERa questionnaire

^aD-MER: dysphoric milk ejection reflex.