title: Very preterm infants show earlier emergence of 24-hour sleep-wake rhythms compared to term infants.
abstract: 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.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  Prospective cohort study with nested interventional trial.
  
  
  METHODS
  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].
  
  
  METHODS
  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. Trial registry number: This trial has been registered at www.clinicaltrials.gov (identifier NCT01513226).
authors.affiliation: Child Development Center, Department of Pediatrics, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland.
authors.forename: Caroline
authors.initials: C
authors.lastname: Guyer
authors.affiliation: Child Development Center, Department of Pediatrics, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland; Children's Research Center (CRC), University Children's Hospital Zürich, CH-8032 Zürich, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Huber
authors.affiliation: Clinic Neonatology, University Hospital Zürich, CH-8091 Zürich, Switzerland.
authors.forename: Jehudith
authors.initials: J
authors.lastname: Fontijn
authors.affiliation: Clinic Neonatology, University Hospital Zürich, CH-8091 Zürich, Switzerland.
authors.forename: Hans Ulrich
authors.initials: HU
authors.lastname: Bucher
authors.affiliation: Clinic Neonatology, University Hospital Zürich, CH-8091 Zürich, Switzerland.
authors.forename: Heide
authors.initials: H
authors.lastname: Nicolai
authors.affiliation: Child Development Center, Department of Pediatrics, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland; Department of Psychosomatics and Psychiatry, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland.
authors.forename: Helene
authors.initials: H
authors.lastname: Werner
authors.affiliation: Child Development Center, Department of Pediatrics, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland.
authors.forename: Luciano
authors.initials: L
authors.lastname: Molinari
authors.affiliation: Child Development Center, Department of Pediatrics, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland; Children's Research Center (CRC), University Children's Hospital Zürich, CH-8032 Zürich, Switzerland.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Latal
authors.affiliation: Child Development Center, Department of Pediatrics, University Children's Hospital Zürich, CH-8032 Zürich, Switzerland; Children's Research Center (CRC), University Children's Hospital Zürich, CH-8032 Zürich, Switzerland. Electronic address: Oskar.Jenni@kispi.uzh.ch.
authors.forename: Oskar G
authors.initials: OG
authors.lastname: Jenni
mesh_terms: D000204:Activity Cycles; D005260:Female; D006801:Humans; D062071:Infant, Extremely Premature / Q000502:physiology*; D007231:Infant, Newborn; D008297:Male; D012890:Sleep
keywords: Actigraphy; Circadian rhythm; Light; Preterm; Sleep