Eat, sleep, repeat: longitudinal analyses of early postpartum factors, infant sleep, human milk feeding mode, and exclusive expression in the Infant Feeding Practices Study (IFPS-II)

Abstract

Human milk (HM) is widely accepted as the ideal nutrition for newborns and infants, and professional organizations worldwide recommend exclusive HM feeding for the first 6 months postpartum followed by predominant HM feeding through the 1st year and complementary HM for the 2nd year and beyond. Only a small proportion receive human milk to meet these guidelines, with meaningful health consequences.While lactation is a physiological process, human milk feeding is a complex socio-cultural behavior that impacts, and is impacted by, many factors. The aims of this thesis were to identify supports of and barriers to sustained human milk feeding in the first year postpartum using data from the Infant Feeding Practices Study II (IFPS-II). The IFPS-II is the largest longitudinal dataset with detailed information on postpartum behaviors and experiences related to infant feeding in the United States. Leveraging this comprehensive dataset, this dissertation investigated the impact of the timing of infant sleep consolidation, colloquially referred to as when an infant ‘sleeps through the night’, on subsequent cessation of HM feeding. Additional analyses utilized the same dataset to examine factors related to infant feeding mode, defined based on the proportion of milk feeds that infants receive as expressed (pumped) HM and as HM transferred directly from parent to infant at the breast. The primary findings are (1) earlier infant sleep consolidation is associated with a lower hazard of cessation of any human milk feeding, (2) exclusive HM expression is associated with a shorter duration of human milk feeding and is associated with peripartum in-patient hospital experiences, and (3) among exclusive expressors there are key differences in the feeding experiences and outcomes for parent-infant dyads based on their duration of milk expression over the first six months postpartum. Taken together, these results point to particular early infant feeding and sleep patterns, and early postpartum in-patient hospital practices, that support or hinder sustained human milk feeding in the United States population. In summary, my findings contribute to the understanding of supports and barriers to human milk feeding by examining infant sleep, modes of human milk feeding, and duration of human milk feeding. Two of my manuscripts have a particular focus on those who are expressing all or most of the human milk their infant consumes. Almost all parents who are feeding their infants human milk now pump at least some of the time, and international trends suggest the practice of exclusive expression is increasingly common. Therefore, these findings can inform public health interventions, clinical practice, and health policy to support this group of parents.