An evolutionarily informed perspective on parent-infant sleep contact challenges recommendations regarding appropriate parent-infant sleep practices based on large epidemiological studies. In this study regularly bed-sharing parents and infants participated in an in-home video study of bed-sharing behavior. Ten formula-feeding and ten breast-feeding families were filmed for 3 nights (adjustment, dyadic, and triadic nights) for 8 hours per night. For breast-fed infants, mother-infant orientation, sleep position, frequency of feeding, arousal, and synchronous arousal were all consistent with previous sleep-lab studies of mother-infant bed-sharing behavior, but significant differences were found between formula and breast-fed infants. While breast-feeding mothers shared a bed with their infants in a characteristic manner that provided several safety benefits, formula-feeding mothers shared a bed in a more variable manner with consequences for infant safety. Paternal bed-sharing behavior introduced further variability. Epidemiological case-control studies examining bed-sharing risks and benefits do not normally control for behavioral variables that an evolutionary viewpoint would deem crucial. This study demonstrates how parental behavior affects the bed-sharing experience and indicates that cases and controls in epidemiological studies should be matched for behavioral, as well as sociodemographic, variables.
Keywords: Bed-sharing; Breast-feeding; Formula-feeding; Infant sleep; Motherinfant behavior.