title: Comparable risk of childhood asthma after vaginal delivery and emergency caesarean section.
abstract: BACKGROUND
  Caesarean section is thought to be a risk factor for childhood asthma, but this association may be caused by confounding from, for instance, familial factors. To address this problem, we used twin pairs to assess the risk of childhood asthma after emergency caesarean section.
  
  
  METHODS
  The study was a register-based nation-wide matched cohort study using twin pairs to minimise residual confounding. Included were twin pairs in which the first twin was delivered vaginally and the second by emergency caesarean section during the study period from January 1997 through December 2012.
  
  
  RESULTS
  In total, 464 twin pairs (928 twins) were included. In 30 pairs, the first twin (vaginal delivery) was diagnosed with asthma, but the second twin (emergency caesarean section) was not. In 20 pairs, the second twin (emergency caesarean section) was diagnosed with asthma, but the first twin (vaginal delivery) was not. In 11 pairs, both twins developed asthma. In the unadjusted analysis, emergency caesarean section did not affect the risk of asthma (odds ratio = 0.67 (95% confidence interval: 0.38-1.17); p = 0.16). After adjusting for birth weight, gender, umbilical cord pH, Apgar score at 5 min. and neonatal respiratory morbidity, the risk of childhood asthma following emergency caesarean section remained unchanged.
  
  
  CONCLUSIONS
  Emergency caesarean section was not associated with childhood asthma.
  
  
  BACKGROUND
  none.
  
  
  BACKGROUND
  not relevant.
authors.affiliation: nis.brix@gmail.com.
authors.forename: Nis
authors.initials: N
authors.lastname: Brix
authors.forename: Lonny
authors.initials: L
authors.lastname: Stokholm
authors.forename: Fjola
authors.initials: F
authors.lastname: Jonsdottir
authors.forename: Kim
authors.initials: K
authors.lastname: Kristensen
authors.forename: Niels Jørgen
authors.initials: NJ
authors.lastname: Secher
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000453:epidemiology / Q000209:etiology*; D002585:Cesarean Section; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D004630:Emergencies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D036801:Parturition; D012042:Registries; D018570:Risk Assessment