title: Chronobiology of labour pain perception: an observational study.
abstract: BACKGROUND
  Circadian variation may affect many biological and pharmacological phenomena.
  
  
  METHODS
  To assess circadian variations in labour pain perception, 222 consecutive nulliparous women with uncomplicated pregnancy, spontaneous labour, cervical dilatation (3-5 cm), ruptured membranes and normal fetal heart rate tracings were studied. Visual analogue pain scores (VAPS) were analysed and divided into four periods: night (1:01 a.m. to 7:00 a.m.), morning (7:01 a.m. to 1:00 p.m.), afternoon (1:01 p.m. to 7:00 p.m.) and evening (7:01 p.m. to 1:00 a.m.). VAPS were also compared between daytime (morning+afternoon) and nocturnal (evening+night) periods.
  
  
  RESULTS
  Daytime mean VAPS were lower than nocturnal scores [75.6 (15.1) vs 85.7 (14.1), P<0.0001]. VAPS were lower in the morning than in the afternoon, evening and night periods (anova, P<0.0001).
  
  
  CONCLUSIONS
  Labour pain perception appears to be chronobiological, and this might be taken into account when enrolling parturients in studies designed to assess or treat labour pain.
authors.affiliation: Division of Anesthesiology, Pain Management, Emergency and Critical Care Medicine, University Hospital, Nîmes, France. guy.aya@chu-nimes.fr
authors.forename: A G M
authors.initials: AG
authors.lastname: Aya
authors.forename: N
authors.initials: N
authors.lastname: Vialles
authors.forename: R
authors.initials: R
authors.lastname: Mangin
authors.forename: C
authors.initials: C
authors.lastname: Robert
authors.forename: J M
authors.initials: JM
authors.lastname: Ferrer
authors.forename: J
authors.initials: J
authors.lastname: Ripart
authors.forename: J E
authors.initials: JE
authors.lastname: de La Coussaye
mesh_terms: D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D007743:Labor, Obstetric / Q000523:psychology*; D010146:Pain / Q000503:physiopathology / Q000523:psychology*; D010147:Pain Measurement / Q000379:methods; D010465:Perception / Q000502:physiology*; D011247:Pregnancy