title: Risk of asthma in young adults who were born preterm: a Swedish national cohort study.
abstract: OBJECTIVE
  Preterm birth is associated with asthma-like symptoms in childhood and possibly in adolescence, but the longer-term risk of asthma is unknown and increasingly relevant as larger numbers of these individuals enter adulthood. Our objective was to evaluate whether those who were born preterm are more likely to be prescribed asthma medications in young adulthood than those who were born term.
  
  
  METHODS
  We conducted a national cohort study of all singleton infants born in Sweden from 1973 through 1979 (n = 622 616), followed to ages 25.5 to 35.0 years to determine whether asthma medications were prescribed in 2005-2007. Asthma medication data were obtained from all outpatient and inpatient pharmacies throughout Sweden. To improve the positive predictive value for asthma, the outcome was defined as prescription of (1) both a β-2 agonist inhalant and a glucocorticoid inhalant or (2) a combination inhalant containing a β-2 agonist and other drugs for obstructive airway diseases.
  
  
  RESULTS
  Young adults who were born extremely preterm (23-27 weeks' gestation) were 2.4 times more likely (adjusted 95% CI: 1.41-4.06) to be prescribed asthma medications than those who were born term. No association was found between later preterm birth (28-32 or 33-36 weeks' gestation) and asthma medications in young adulthood.
  
  
  CONCLUSIONS
  This is the first study with sufficient statistical power to evaluate the risk of asthma beyond adolescence in individuals who were born extremely preterm. The results suggest that extreme preterm birth (23-27 weeks' gestation), but not later preterm birth, is associated with an increased risk of asthma at least into young adulthood.
authors.affiliation: Department of Medicine, Stanford University, Palo Alto, California, USA. kccrump@stanford.edu
authors.forename: Casey
authors.initials: C
authors.lastname: Crump
authors.forename: Marilyn A
authors.initials: MA
authors.lastname: Winkleby
authors.forename: Jan
authors.initials: J
authors.lastname: Sundquist
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
mesh_terms: D000293:Adolescent; D000328:Adult; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use; D001249:Asthma / Q000188:drug therapy / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006306:Health Surveys; D006801:Humans; D007223:Infant; D052577:Infant, Extremely Low Birth Weight; D007231:Infant, Newborn; D007235:Infant, Premature, Diseases / Q000188:drug therapy / Q000453:epidemiology*; D019102:Infant, Very Low Birth Weight; D008137:Longitudinal Studies; D008297:Male; D011247:Pregnancy; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors; D013548:Sweden; D055815:Young Adult
chemical_list: D018927:Anti-Asthmatic Agents