title: Delivery by caesarean section and childhood cancer: a nationwide follow-up study in three countries.
abstract: OBJECTIVE
  To investigate the association between delivery by caesarean section and risk of childhood cancer.
  
  
  METHODS
  A population-based, follow-up study using register data from three countries.
  
  
  METHODS
  Denmark, Sweden and Finland.
  
  
  METHODS
  Children born in Denmark (1973-2007), Sweden (1973-2006) and Finland (randomly selected sample of 90%, 1987-2007; n = 7,029,843).
  
  
  METHODS
  Exposure was delivery by caesarean section and the outcome was childhood cancer diagnosis. Follow-up started from birth and ended at the first of the following dates: cancer diagnosis, death, emigration, day before 15th birthday or end of follow-up. Cox regression was used to obtain hazard ratios.
  
  
  METHODS
  Childhood cancer diagnosis.
  
  
  RESULTS
  A total of 882,907 (12.6%) children were delivered by caesarean section. Of these, 30.3% were elective (n = 267,603), 35.9% unplanned (n = 316,536) and 33.8% had no information on planning (n = 298,768). Altogether, 11,181 children received a cancer diagnosis. No evidence of an increased risk of childhood cancer was found for children born by caesarean section (hazard ratio, 1.05; 95% confidence interval, 0.99, 1.11). No association was found for any major type of childhood cancer, or when split by the type of caesarean section (elective/unplanned).
  
  
  CONCLUSIONS
  The evidence does not suggest that caesarean section is a risk factor for the overall risk of childhood cancer and possibly not for subtypes of childhood cancer either.
authors: Section for Epidemiology, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors: N C
authors: NC
authors: Momen
authors: J
authors: J
authors: Olsen
authors: M
authors: M
authors: Gissler
authors: S
authors: S
authors: Cnattingius
authors: J
authors: J
authors: Li
mesh_terms: D002585:Cesarean Section / Q000009:adverse effects / Q000706:statistics & numerical data*; D002648:Child; D002675:Child, Preschool; D003718:Denmark; D005260:Female; D005387:Finland; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009369:Neoplasms / Q000453:epidemiology* / Q000209:etiology; D011247:Pregnancy; D016016:Proportional Hazards Models; D012307:Risk Factors; D013548:Sweden
keywords: Caesarean section; childhood cancer; follow-up studies; mode of delivery; risk