Very preterm infants show earlier emergence of 24-hour sleep–wake rhythms compared to term infants

•Preterms show longer nighttime sleep than term infants in the first 3 months.•Preterms exhibit less nocturnal activity than term infants in the first 3 months.•Cycled light during neonatal care favours regular sleep–wake rhythms in preterms.•Preterm infants benefit from an early exposure to time cues.

BackgroundPrevious studies show contradictory results about the emergence of 24-h rhythms and the influence of external time cues on sleep–wake behavior in preterm compared to term infants.AimsTo examine whether very preterm infants (< 32 weeks of gestational age) differ in their emergence of the 24-h sleep–wake rhythm at 5, 11 and 25 weeks corrected age compared to term infants and whether cycled light conditions during neonatal intermediate care affects postnatal 24-h sleep–wake rhythms in preterm infants.Study design: Prospective cohort study with nested interventional trial.Subjects: 34 preterm and 14 control term infants were studied. During neonatal hospitalization, preterm infants were randomly assigned to cycled light [7 am–7 pm lights on, 7 pm–7 am lights off, n = 17] or dim light condition [lights off whenever the child is asleep, n = 17].Outcome measures: Sleep and activity behavior recorded by parental diary and actigraphy at 5, 11 and 25 weeks corrected age.ResultsSleep at nighttime and the longest consolidated sleep period between 12 pm-6 am was longer (mixed model analysis, factor group: p = 0.02, resp. p = 0.01) and activity at nighttime was lower (p = 0.005) at all ages in preterm compared to term infants. Cycled light exposed preterm infants showed the longest nighttime sleep duration. Dim light exposed preterm infants were the least active.ConclusionsPreterm infants show an earlier emergence of the 24-h sleep–wake rhythm compared to term infants. Thus, the length of exposure to external time cues such as light may be important for the maturation of infant sleep–wake rhythms.Trial registry number: This trial has been registered at www.clinicaltrials.gov (identifier NCT01513226).

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