This review investigates development in the durations of infants' capabilities for sustained sleep across their first year, a matter of interest to clinicians, parents and researchers. It describes three aspects of sleep development: longest sustained sleep period (sleep sustained without awakening), longest self-regulated sleep period (behavioural quietude including sleep and quiet awakenings), and sleeping through the night (a predetermined nocturnal period). Clear trends were evident despite methodological differences making comparison between studies difficult. The most marked changes were across the first 4 months, particularly ages 1 and 2 months. Minimal changes followed through to 9 months and a small increase in all but the longest sustained sleep period, until age 12 months. Moore and Ucko's early, yet influential definition for sleeping through the night (24:00-05:00 h) may have underestimated infants' capacities for uninterrupted sleep. Infants do meet more stringent criteria and most can sleep 8 h by age 6 months and 9 or more hours thereafter. These findings have implications for clinicians addressing parental concerns around developmentally appropriate expectations of infant sleep. Researchers now have sufficient evidence to identify developmentally sensitive timing for preventive interventions for infant sleep disturbance.
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