Introduction Recent Interest in the Physiologic and Behavioral Correlates of Mother-infant Bed Sharing Is Driven, in Part, by Claims That Bed Sharing Is a Significant Independent Risk Factor for the Sudden Infant

RECENT INTEREST IN THE PHYSIOLOGIC AND BEHAVIORAL CORRELATES OF MOTHER-INFANT BED SHARING IS DRIVEN, IN PART, BY CLAIMS THAT BED SHARING IS A SIGNIFICANT INDEPENDENT RISK FACTOR FOR THE SUDDEN INFANT DEATH SYNDROME (SIDS).1 Furthermore, some form of co-sleeping or bed sharing represents the condition under which infants adapted throughout human evolutionary history.2,3 It seems self-evident that the infant’s sensory and social environment during bed sharing is enriched compared to that found during solitary sleeping. It is much less clear whether the physiologic differences between infants in the 2 conditions, presumably related to those environmental differences, are clinically relevant. In terms of infant morbidity and mortality, the various physiologic responses and adaptations to bed sharing that have been previously reported could be construed as positive (increased breast-feeding and arousal frequency, less obstructive apnea, greater maternal vigilance4-7), negative (increased central apnea and periodic breathing and, from a SIDS perspective, higher body temperature in non-rapid eye movement sleep [REM]6,8,9). or neutral (as with small, but statistically significant differences in sleep architecture10). Understanding the effects of bed sharing on infant heart rate might be useful in determining how stimuli related to the presence of the mother could affect homeostatic systems during this important developmental period. Increases in basal heart rate can indicate increases in sympathetic relative to parasympathetic activity, and decreases in heart-rate variability can indicate possible cardiovascular control-system insufficiency.11,12 In addition, Petersen et al13 suggested that developmental changes in infant heart rate are related to developmental changes in the thermoregulatory system. Infant body temperature is significantly affected by bed sharing versus solitary sleeping, probably with a sleepstage effect8,9; therefore, it is possible that bed sharing could affect heart rate via its effect on thermoregulation. Since external sensory input is generally arousing and involves increased sympathetic activity,14,15 we hypothesized that infant heart rate would be increased during mother-infant bed sharing. In the absence of prior findings that would predict a specific effect of enhanced sensory input on heart-rate variability, we proposed the null hypothesis, ie, that heart-rate variability would not differ in the 2 environments.