title: The burden of childhood asthma and late preterm and early term births.
abstract: OBJECTIVE
  To evaluate the association between gestational age at birth and the risk of subsequent development of asthma.
  
  
  METHODS
  We conducted a retrospective observational hospital-based birth case-control study in a university-based obstetrics and gynecology department in Finland. A total of 44,173 women delivering between 1989 and 2008 were linked with the social insurance register to identify asthma reimbursements for their offspring (n = 2661). Pregnancy factors were recorded during pregnancy. Infants were categorized as moderately preterm (≤ 32 weeks), late preterm (33-36 weeks), early term (37-38 weeks), term (39-40 weeks), or late term and postterm (≥ 41 weeks). The main outcome measure was asthma among the infants.
  
  
  RESULTS
  Children born moderately preterm (≤ 32 weeks gestation) had a significantly increased risk of asthma (aOR, 3.9; 95% CI, 3.2-4.8). The risk of asthma was also increased in those born late preterm (aOR, 1.7; 95% CI, 1.4-2.0) and early term (aOR, 1.2; 95% CI, 1.1-1.4). In contrast, delivery at 41 weeks or later seemed to decrease the risk of asthma (aOR, 0.9; 95% CI, 0.8-1.0). The burden of asthma associated with preterm birth was associated mainly with early term infants, in whom 108 extra cases of asthma were observed.
  
  
  CONCLUSIONS
  Even though the individual risk of asthma was inversely correlated with gestational age at birth, the overall burden brought about by delivery before term was associated with late preterm and early term deliveries. Furthermore, delivery after term was protective against asthma.
authors.affiliation: Department of Obstetrics and Gynecology, Kuopio University Hospital, Kuopio, Finland. Electronic address: maijakaisa.harju@kuh.fi.
authors.forename: Maijakaisa
authors.initials: M
authors.lastname: Harju
authors.affiliation: Department of Obstetrics and Gynecology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Leea
authors.initials: L
authors.lastname: Keski-Nisula
authors.affiliation: Department of Obstetrics and Gynecology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Leena
authors.initials: L
authors.lastname: Georgiadis
authors.affiliation: Department of Obstetrics and Gynecology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Sari
authors.initials: S
authors.lastname: Räisänen
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland; Nordic School of Public Health, Gothenburg, Sweden.
authors.forename: Mika
authors.initials: M
authors.lastname: Gissler
authors.affiliation: Department of Obstetrics and Gynecology, Kuopio University Hospital, Kuopio, Finland; Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland.
authors.forename: Seppo
authors.initials: S
authors.lastname: Heinonen
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007235:Infant, Premature, Diseases / Q000453:epidemiology*; D008297:Male; D009017:Morbidity / Q000639:trends; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012042:Registries; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012959:Socioeconomic Factors; D055815:Young Adult
keywords: ART; Assisted reproduction technology