Objective To determine the association between large birth weight and the risk of developing asthma in early childhood.
Methods All single live births (n=687 194) born in Ontario between 1 April 1995 and 31 March 2001 were followed until their sixth birthday. Their birth weight was categorised as low (<2.5 kg), normal (2.5–4.5 kg), large (4.6–6.5 kg) or extremely large (>6.5 kg). Poisson regression analysis was used.
Results Compared with normal-birth-weight infants, large-birth-weight infants (2.3% of total) had a slightly lower risk of developing asthma by age 6 after adjusting for confounders (adjusted RR 0.90, 95% CI 0.86 to 0.93). There was a trend towards increased risk of asthma among extremely large-birth-weight infants (RR 1.21, 95% CI 0.67 to 2.19).
Conclusions Contrary to previous reports, large birth weight was associated with a lower risk for asthma. Instead, a trend towards increased risk of asthma was observed among extremely large-birth-weight infants and interventions to reduce the incidence of extreme large birth weight may help reduce the risk of asthma.
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Funding This study was supported by the Canadian Allergy, Asthma and Immunology Foundation. TT is supported by the University of Toronto, Life Sciences Committee, Dales Award in Medical Research. ASG was supported by the Canadian Institutes of Health Research through a Research Fellowship Award and is currently supported by the Government of Ontario through a Career Scientist Award. DR is supported by the Ontario Thoracic Society and the Research Training Competition Award from the Research Institute, The Hospital for Sick Children. This study was supported by the Institute for Clinical Evaluative Sciences, an independent non-profit organisation funded by the Government of Ontario, with provision of population-based data.
Competing interests None.
Ethics approval Ethics approval was provided by the Research Ethics Boards of Hospital for Sick Children in Toronto and Institute for Clinical Evaluative Sciences, Ontario.
Provenance and peer review Not commissioned; externally peer reviewed.