Reference values and changes in infant sleep-wake behaviour during the first 12 months of life: a systematic review

This paper is a systematic review on the reference values and changes in infant sleep-wake behaviour during the first 12 months of life. This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Seventy-four papers were included, and the reference values and changes in sleep-wake behaviour during the first 12 months of life were identified. Sleep duration during the 24-h period, and day and sleep periods during the night decreased over the first 12 months of life. Night wakings and bedtime/sleep-onset time decreased, while the longest sleep period increased at night during the first 6 months. High discrepancy was noted between studies in the reference values of sleep-wake behaviour, while more congruence was noted regarding changes, especially those occurring in the first 6 months of life. Several methodological differences were identified between studies and may partially explain inconsistencies in the results, including the assessment of different sleep-wake behaviours, the focus on specific ages or age ranges, the use of self-report, observational or direct measures, the recruitment of small or large representative samples, and the countries where the research was conducted. These aspects should be considered in future research and caution should be taken when generalizing results from studies with diverse methodological characteristics. Nonetheless, this review identifies normative reference values and the changes occurring in infant sleep-wake behaviour, and could inform both practitioners and researchers, helping them identify infants with sleep delays or problems.