Observational studies in the home, hospital and laboratory have produced remarkably consistent information about the way in which mothers and infants behave in a bed-sharing environment (Richard, Mosko, McKenna,& Drummond, 1996; Baddock et al, 2006, 2007; Ball 2001, 2006a, 2006b).
The cumulative results of these studies provide a robust understanding of breastfeeding-related bed-sharing behaviour and suggest that mothers' characteristic sleep position represents an instinctive behaviour on the part of a breastfeeding mother to protect her baby during sleep.
Mother-baby dyads who routinely bed-share and breastfeed sleep in close proximity with a high degree of mutual orientation (facing one another) and arousal overlap (waking at the same time). In recent years studies have shown breastfeeding dyads displaying consistent bed-sharing behaviour regardless of whether they slept in a narrow hospital bed, a full-size bed in a sleep lab, or at home in beds ranging from twin to king-sized (Baddock et al 2006; Ball 2006a, 2006b; Young et al 2001). Although this behaviour evolved in a very different sleep context than one adorned with Western beds and bedding, the principle of infant protection is no less effective. Breastfeeding mothers instinctively place their infants supine, level with their breasts, on the mattress surface (below the level of any pillows). Mothers assume a protective position in the bed - curled around the infant in a 'C' shape, with her arm above the infant's head and her knees drawn up under its feet, she thus protects it from environmental hazards - cold; heat; bedding and bed-partners.
Mothers and infants tend to face each other during the night; they remain close - within touching distance - at all times; and mothers and infants experience increased sleep synchrony compared to sleeping apart (Baddock et al 2006; Ball 2006a, 2006b; Richard & Mosko 1996).
There has been comparatively little research into co-sleepers' sleep quality; Volkovich et al. (2015) reported that co-sleeping mothers objectively and subjectively had significantly worse sleep than solitary sleeping mothers when their infants were both three and six months old. This included more night-wakings, longer wakefulness during the night and shorter duration of sleep periods. This may be a result of heightened awareness of one’s baby and increased breastfeeding. Infant sleep quality is also perceived to be lower, again possibly being breastfeeding related, and that co-sleeping mothers are more aware of their infant during the night and more responsive to their movements and vocalisations, which is ultimately safer for the infant. Both mothers and infant who sleep in close proximity experience less time in deep sleep and more micro-arousals throughout the night, which is considered protective (Mosko et al 1997).