Establishing Global Reference Values for Human Milk Composition in a Multi-Center Collaborative Study

The investigators will collect breast milk samples at four visits, at 2-3 days after birth (colostrum) and at 1-3.4, 3.5-5.9, and 6-8.5 months of lactation from well-nourished mothers age ≥18 to ≤40 years, in a systematic, identical way in four countries. The four sites are: Copenhagen, Denmark; Banjul, The Gambia; Rio de Janeiro, Brazil; and Mirpur, Dhaka, Bangladesh. The most important site selection criteria were that multiple micronutrient supplements are not consumed after week 28 of pregnancy; maternal diet is adequate but consumption of highly fortified foods is limited; and exclusive breastfeeding is 60% at 4 months.

In order to have 250 women and infants per site complete the study at 8.5 months, approximately 500 women will be recruited during the third trimester of pregnancy. This should allow for mothers and infants not meeting study eligibility criteria in pregnancy or early lactation, and drop-outs from the study. Recruitment during pregnancy will increase the opportunity to locate and recruit women since recruitment in the immediate post-delivery period will be difficult. It will also enable the women to be counselled on the importance of exclusive breastfeeding (EBF). Colostrum will be collected at 2-3 days postpartum for future analysis. The first collection of mature milk will occur between 1 and 3.4 months postpartum, when maternal and infant blood samples will also be collected on all participants. At the final two visits, in addition to milk collection, blood will be taken from all mothers but only half of the infants each time, primarily for the assessment of micronutrient status.

A requirement is that infants must be EBF in the 1-3.4 month period, and breastfed (BF) in the second and third period. Longitudinal measurements on the same mother after the BF period are not necessary for statistical reasons, as the investigators are not creating RVs for change in milk composition. The investigators expect that due to attrition and cessation of BF, the sample size will need to be augmented in later months; the alternative would have been to recruit and measure many more women in earlier stages in order to have an adequate sample size in the 7-8.5 month interval, which would be a much less efficient approach. Therefore after 6 months, if women are not breastfeeding, additional lactating women will be recruited from the group that was not EBF in the 3.4 month period, or from the local health center or community.

At all three points of mature milk collection the investigators will measure breast milk volume; diet, anthropometry and morbidity of the mother and infant; and infant development at 3.5-5.9 and 6 to 8.5 months; and will collect infant fecal samples for future analyses of the microbiome. Milk volume will be measured at three sites using the International Atomic Energy Agency's protocol that requires dosing the mother with deuterated water and collecting maternal and infant saliva urine samples at 0, 1, 2, 3, 4, 13 and 14 days after the dose. In Denmark breast milk volume will be measured by 24 hour infant weighing.

Most of the laboratory analyses will be conducted at the United States Department of Agriculture, Agricultural Research Service, Western Human Nutrition Research Center (WHNRC) in Davis, California. Other analyses will be performed in the Department of Chemistry at University of California, Davis (HMOs and other bioactive compounds in milk), and the Swiss Federal Institute of Technology in Zurich (iodine status). RVs will be constructed following the methods and principles developed for the World Health Organization (WHO) Child Growth Standards and the Intergrowth-21st Project.