title: Time of birth and risk of intrapartum and early neonatal death.
abstract: BACKGROUND
  Previous studies have found that infants born at night and during weekends and holidays have an increased risk of perinatal mortality. However, these associations may be confounded by the distribution of high-risk deliveries according to time of birth.
  
  
  METHODS
  We undertook a population-based cohort study of 694,888 singleton births without elective cesarean section in Sweden between 1991 and 1997. We estimated relative risks of intrapartum and early neonatal death according to the hour, day and month of delivery. Estimated risk ratios were adjusted for gestational age, birth weight for gestational age, malformations, induction of labor, breech presentations and year of birth.
  
  
  RESULTS
  Infants of high-risk deliveries were more often delivered during daytime (8:00 am to 7:59 pm). Compared with infants born during daytime, infants born at night were at increased risk of early neonatal death (adjusted risk ratio = 1.28; 95% confidence interval = 1.13-1.46), but not intrapartum death (1.05; 0.71-1.54). If this association is causal, 12% of early neonatal deaths can be attributed to the increased risk among nighttime births. There was no association of weekend or holiday births with risks of intrapartum or early neonatal death.
  
  
  CONCLUSIONS
  Infants born at night may be at increased risk of early neonatal death.
authors.affiliation: Department of Medical Epidemiology, Karolinska Institute, Stockholm, Sweden. olof.stephansson@mep.ki.se
authors.forename: Olof
authors.initials: O
authors.lastname: Stephansson
authors.forename: Paul W
authors.initials: PW
authors.lastname: Dickman
authors.forename: Anna L V
authors.initials: AL
authors.lastname: Johansson
authors.forename: Helle
authors.initials: H
authors.lastname: Kieler
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
mesh_terms: D015331:Cohort Studies; D005260:Female; D005313:Fetal Death; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D016015:Logistic Models; D011247:Pregnancy; D012042:Registries; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors