Selection of subjects for human milk surveillance and research studies.

Subject selection for studies investigating environmental chemicals in human milk requires thoughtful consideration of multiple factors. Studies often need to produce generalizable and representative data that can be compared to other similar studies. Goals of the study determine the selection of subjects. Exposure is only one factor that influences the levels of environmental chemicals in human milk. Many maternal and infant characteristics should be considered in subject selection. Collection procedures of human milk samples also affect subject selection, as subject burden may be enough to reduce compliance with the collection protocols. Decisions must be made about pooling of samples both within subjects and within populations. Guidelines for subject selection are provided by the World Health Organization for human milk monitoring, but distinct differences in the lactational practices, geography, and ethnic and racial diversity of the U.S. population require somewhat different approaches.