BACKGROUND: Previous 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.
AIMS: To examine whether very preterm infants (<32weeks of gestational age) differ in their emergence of the 24-h sleep-wake rhythm at 5, 11 and 25weeks 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 [7am-7pm lights on, 7pm-7am 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 25weeks corrected age.
RESULTS: Sleep at nighttime and the longest consolidated sleep period between 12pm-6am 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.
CONCLUSIONS: Preterm 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).