Clinical ReviewNormal sleep patterns in infants and children: A systematic review of observational studies
Introduction
Sleep-wake regulation and sleep states evolve rapidly during the first year of life with continued maturation across childhood. Because newborns do not have an established circadian rhythm, their sleep is distributed throughout the day and night with each period of sleep short because of feeding frequency.1 At around 10–12 weeks of age, the circadian rhythm begins to emerge, and infant sleep becomes increasingly nocturnal.2 Parents can aid the development of a regular nocturnal sleep pattern by facilitating social cues to sleep (e.g., by implementing consistent feed times and bed-time routines).1 Between the ages of 1 and 4 years, children continue to take daytime naps in order achieve their sleep requirements.3 Night wakings are common in infancy and early childhood. A variety of factors influence these but children's ability to return to sleep unaided plays a major role in determining whether or not wakings will persist and become problematic.4 The frequency of night wakings is one of the main factors by which parents judge the quality of their child's sleep.5 By age 5, daytime napping ceases and overnight sleep duration gradually declines throughout childhood, due to a shift to later bedtimes, with wake times remaining stable during the routine week.3 However, sleep-wake patterns, driven by a complex interplay between biological processes, and environmental, behavioural and social factors, can vary widely. In infants and children, for example, daycare and school schedules, parenting practices and expectations, family routines and cultural practices, will all strongly influence sleep and timing. Added to this are individual differences in genetic make-up influencing sleep–wake regulation.
Measurement of sleep in infants and children can be subjective or objective. Subjective data are considered here, from sleep diaries or questionnaires filled out by the caregiver, or asked about in a structured interview. Across studies, several forms of sleep diaries have been used and adapted.6, 7 Diaries have been shown to have a good correlation with objective measures recording sleep schedules over 24-h periods in the home, or for a designated number of days/weeks. However diaries are not so accurate for recording night waking; parents do not always recognise infant awakenings in which the infant has self soothed back to sleep and not audibly awoken.8 There are many questionnaires, some of which are validated such as the Children's Sleep Habits Questionnaire and the Brief Infant Sleep Questionnaire.9 The majority cover questions addressing universal sleep measures of bedtime, wake time and sleep duration and may or may not cover both weekday and weekend schedules.
An accurate description of normal sleep patterns in infants and children necessitates measurement and documentation of sleep patterns and requirements over a long period of rapid maturation, allowing for normal development, and in apparently healthy subjects. Data from prospective observational studies of longitudinal, or cross-sectional design can be used to portray this. Smaller studies can add to the datasets, but carry less weight. Extracting data from studies conducted after 1990 is necessary to relate the information to the current era because sleep duration (an indicator of sleep need) has apparently decreased across time probably in relation to modern lifestyle changes.*3, 10 However a recent systematic review of the evidence that children are sleeping less has been challenged; Mattricani et al.11 found the evidence to be conflicting, of low methodological quality, and specific to particular populations.
As far as we are aware, no systematic reviews have been published specifically for infants and children. One covers objective polysomnographic measures from age 5 across the lifespan.12 The usefulness of collating a systematic review is to provide a standard against which abnormal sleep patterns can be measured, to in turn inform policy and strategies for intervention, and to contribute to and advance our knowledge regarding developmental patterns of sleep. We have extracted and summarized age-specific data from sleep measures in relation to the quantity of sleep over a 24-h period, the number of episodes of waking during nocturnal sleep, the time taken to fall asleep (sleep latency), the longest sleep over a 24-h period, and the number of daytime naps.
Section snippets
Methods
The protocol and data extraction was conducted according to the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.13
Database searches
The search criteria from all databases (with duplicates eliminated) rendered 2114 articles (Fig. 2). Of those, 195 were deemed to be of potential interest and downloaded to examine and apply the more stringent inclusion/exclusion criteria. One hundred and forty-five articles were excluded, leaving 50 articles for review. Reasons for exclusion are listed in Fig. 2. During data extraction, a further 16 were excluded because age ranges were too wide or articles contained actigraphy data only that
Discussion
The main purpose of this systematic review was to provide mean reference values for normative sleep patterns in children from 0 to 12 years. Because the meta-analysis combined data from different countries and cultures, the reference values should be considered as international norms, rather than culture-specific norms. The quality of the data reported here cannot go beyond the quality of the individual studies included, and therefore cannot fully represent all studies published, as many did
Acknowledgements
The Accident Compensation Corporation (ACC) of New Zealand funded the research. The funders had no role in the study design other than to specify the systematic nature and standard of the review. They had no role in data collection, data analysis, data interpretation or writing of the report. BG had full access to all the data in the study and had final responsibility for the decision to submit for publication. Views and/or conclusions in this article are those of the authors and may not
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