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

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 (<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. Results: Sleep 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. 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. (C) 2014 Elsevier Ireland Ltd. All rights reserved.