This observational study is a sub-study of the MiLC Trial (ClinicalTrials.gov Identifier: NCT03123874). Our objective is to characterize the bacterial communities of women's breasts, hands, their pump and milk collection kit, and their babies' mouths among the participants of the MiLC Trial. As part of the original protocol, we collected swabs of each of these areas from each dyad before women pumped with their own pumps. By characterizing these communities, we can identify from where the bacteria in human milk (HM) originates, and determine whether pumping with mother's own pumps enriches the bacterial communities of HM compared to pumping with a sterile pump.