Effects of birth weight and growth on childhood wheezing disorders: findings from the Born in Bradford Cohort

OBJECTIVES To examine the effects of birth weight and childhood growth on childhood wheezing disorders. We hypothesised that low birth weight and fast growth during early age would increase the risk of wheezing disorders. SETTING Observational secondary analysis of data from the Born in Bradford cohort. PARTICIPANTS All children who were born at the Bradford Royal Infirmary hospital between March 2007 and December 2010 were eligible for the study. A total of 13,734 and 1598 children participated in the analyses of the effects of birth weight and growth on wheezing disorders, respectively. PRIMARY AND SECONDARY OUTCOME MEASURES Wheezing disorders diagnosis (diagnosed as asthma or had wheezing symptom) during the ages of 0-7 years were the primary outcome measures. Diagnosis of asthma and occurrence of wheezing during the same period were secondary outcome measures. Birth weight was classified as normal (2.5-4.0 kg), low (<2.5 kg) and high (>4.0 kg). Growth mixture models were used to drive growth pattern outcomes which were classified as 'normal', 'fast' and 'slow' growth based on their velocities between birth and 36 months. RESULTS The adjusted relative risks (RRs) of wheezing disorders diagnosis for the low and high birthweight children were 1.29 (95% CI 1.12 to 1.50; p=0.001) and 0.91 (95% CI 0.79 to 1.04; p=0.17), respectively. The adjusted RRs of wheezing disorders diagnosis were 1.30 (95% CI 0.56 to 3.06; p=0.54) and 0.60 (95% CI 0.16 to 2.18; p=0.44), respectively, for the 'fast' and 'slow' growth as compared with the 'normal' growth. CONCLUSIONS Low birth weight is associated with an increased risk of wheezing disorders; however, there is a weak evidence that suggests high birthweight children have a reduced risk in this birth cohort. Low birth weight coupled with a slower growth until 3 months and a sharp growth between 3 and 12 months has an increased risk of wheezing disorders diagnosis.