title: Perinatal factors and respiratory health in children.
abstract: BACKGROUND
  There is conflicting evidence regarding the associations between anthropometric birth measures and asthma and lung function in children, particularly for apparently healthy infants born at term.
  
  
  OBJECTIVE
  Our objective was to elucidate these relationships paying particular attention to features of study design and analysis that may threaten the validity of previous studies in this field.
  
  
  METHODS
  We analysed data from a cohort of children with a family history of asthma who were recruited antenatally. Anthropometric birth measures and potential confounders were recorded at birth and within the first year of life. Lung function and asthma outcomes were measured at 8 years of age. Airway hyperresponsiveness (AHR) was measured by methacholine challenge. The potential for a reversal paradox, due to inclusion of covariates on the causal pathway, was investigated.
  
  
  RESULTS
  Four hundred and fifty (73% of the initial cohort) children were tested at age 8 years. Birth weight in the lowest tertile was associated with current asthma (OR 1.95, 95% CI 1.08, 3.54) and recent wheeze (OR 1.87, 95%CI 1.08, 3.24), but not with AHR (OR 1.37, 95% CI 0.68, 2.78). Birth weight was positively associated with lung function. Current height modified the relationship between birth length and lung function suggesting that post-natal growth has an effect on this relationship.
  
  
  CONCLUSIONS
  Low birth weight is associated with a greater risk of current asthma and lower lung function at 8 years in children with a family history of asthma. Current height should be treated as an effect modifier when investigating the fetal origins hypothesis.
authors.affiliation: Woolcock Institute of Medical Research, The University of Sydney, Sydney, NSW, Australia. bronwynbrew@woolcock.org.au
authors.forename: B K
authors.initials: BK
authors.lastname: Brew
authors.forename: G B
authors.initials: GB
authors.lastname: Marks
mesh_terms: D001724:Birth Weight; D001837:Body Weights and Measures; D002648:Child; D015331:Cohort Studies; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D016017:Odds Ratio; D012130:Respiratory Hypersensitivity / Q000175:diagnosis / Q000209:etiology*; D012307:Risk Factors; D014797:Vital Capacity