Designing Longitudinal Clinical Studies Involving Lactating Women

In designing longitudinal lactation research studies, certain factors must be taken into account that are necessary for the generation of meaningful data. Perhaps more like longitudinal childhood research studies in terms of ongoing changes that occur during childhood that challenge study design, longitudinal lactation research studies encompass a period of tremendous change in both the mother and her breastfeeding infant that affect study design, implementation, and analysis. Given this changing dynamic, studies should be designed to accommodate a whole host of factors, such as changes in maternal and infant health; coexisting conditions during the lactation period; the stage of lactation; diurnal variations; the frequency and exclusivity of breastfeeding; maternal diet and any complementary/supplementary foods given to the infant; geography; socioeconomic factors; body mass index; physical activity; and any changes in milk composition that occur across longer periods of lactation. The study of human milk composition itself has lacked rigor and any standardization of methods, and has only recently been revisited with more sophisticated laboratory techniques that have allowed a more meaningful understanding of milk structure and biology, with a greater global approach. In this Research Column, we review some of the issues and challenges in conducting longitudinal lactation research, and provide several references that will aid in the development of meaningful study designs and the interpretation of data.