title: Low birth weight and respiratory hospitalizations in adolescence.
abstract: OBJECTIVE
  Some low birth weight survivors are at increased risk of respiratory disease. We studied whether low birth weight was associated with hospitalization for respiratory illness in adolescence and to what degree bronchopulmonary dysplasia, cerebral palsy, and other comorbidities accounted for this association.
  
  
  METHODS
  We performed a population-based retrospective cohort study using Washington State birth certificates from 1987 to 1994 to identify exposed (low birth weight) and unexposed (normal birth weight) subjects. Normal birth weight subjects were randomly selected from birth certificates, frequency matched to low birth weight subjects by birth year. Deaths prior to age 12 were excluded. The primary exposure was low birth weight: subcategorized as moderately-low-birth weight (1,500-2,499 g) and very-low-birth weight (<1,500 g). The primary outcome was the first respiratory related hospitalization between the ages of 12-20. Respiratory hospitalizations were defined by ICD-9 discharge diagnosis codes.
  
  
  RESULTS
  After adjustment, the hazard ratio for hospitalization was 1.39 for moderately-low-birth weight (95% CI 1.17-1.65, P < 0.001) and 2.52 for very-low-birth weight (1.80-3.53, P < 0.001). Controlling for bronchopulmonary dysplasia attenuated the risk for very-low-birth weight to 1.76 (1.17-2.64; P = 0.006). A similar attenuation was seen after controlling for cerebral palsy [HR 1.49 (1.02-2.18), P = 0.04], suggesting that some of the risk is mediated through these diagnoses. Among moderately-low-birth weight survivors, controlling for these diagnoses had less of an effect.
  
  
  CONCLUSIONS
  Low birth weight was associated with an increased risk of respiratory hospitalizations in adolescence. Comorbidities explained some of this risk. However, low birth weight remained independently associated with an increased risk of hospitalization.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, University of Washington, Seattle, Washington; Department of Epidemiology, University of Washington, Seattle, Washington; Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, Washington. ericw@u.washington.edu.
authors.forename: Eric C
authors.initials: EC
authors.lastname: Walter
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Koepsell
authors.forename: Jason W
authors.initials: JW
authors.lastname: Chien
mesh_terms: D002547:Cerebral Palsy / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D005080:Exercise Test; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008297:Male; D012140:Respiratory Tract Diseases / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D014861:Washington / Q000453:epidemiology