Early growth and the risk of childhood asthma: A meta-analysis of 147,000 European children

Background. Low birth weight, preterm birth and rapid infant growth seem to be associated with increased risks of childhood asthma. We examined the association of birth and infant growth characteristics with the risks of preschool wheezing and school age asthma using data from 147,252 subjects of 31 European cohort studies. Methods. Studies were eligible if they included children from 1989 onwards, had information on at least gestational age and weight at birth, and preschool wheezing (1-4 years) or school-age asthma (5-10 years). Adjusted pooled odds ratios (OR) from random effect models were calculated, and ORs from individual participant data were used to assess the combined effect of birth weight and gestational age. Results. Compared with term birth, preterm birth (< 37 weeks) was positively associated with increased risks of preschool wheezing and school-age asthma, independent of birth weight (OR 1.34 (1.25, 1.43) and 1.40 (1.18, 1.67)). Birth weight was not associated with preschool wheezing and school-age asthma after adjustment for gestational age at birth. Infant weight gain was positively associated with preschool wheezing and school-age asthma (OR 1.83 (1.61, 2.08) and 1.62 (1.22, 2.14) per 500 gram weight gain per month). We observed the strongest effects on preschool wheezing and school-age asthma for children born preterm with a high birth weight for gestational age, compared with term born children with an appropriate birth weight for gestational age (OR 2.40 (1.53, 3.75) and 2.77 (1.56, 4.95)). Conclusions. Preterm birth and higher infant weight gain, but not low birth weight, are associated with increased risks of wheezing and asthma in childhood.