Birthweight and the risk of atopic diseases: the ISAAC Phase III study.

Background: The association between birthweight and asthma, eczema and rhinoconjunctivitisis conflicting.

Aims: To examine the association between birthweight and symptoms of asthma, eczema and rhinoconjunctivitis.

Methods: Parents or guardians of children aged 6–7 yr completed written questionnaires about symptoms of asthma, rhinoconjunctivitis and eczema, and several risk factors, including birthweight.

Results: There were 162,324 children from 60 centres in 26 countries. Low birthweight(<2.5 kg) was associated with an increased risk of symptoms of asthma (current wheeze odds ratio = 1.20; 95% confidence interval = 1.12–1.30). Low birthweight was associated with a lower risk of eczema ever. Low birthweight was not associated with rhinoconjunctivitis. Large babies (birthweight ≥4.5 kg) were not associated with any of these outcomes.

Conclusions: This study has confirmed that low birthweight is a risk factor for symptoms of asthma, but not for rhinoconjunctivitis. The findings for eczema are equivocal.