Fetal growth and hospitalization with asthma during early childhood: a follow-up study in Denmark.

BACKGROUND Childhood asthma may have a fetal origin. In order to examine this hypothesis we examined the association between fetal growth indicators and hospitalization with asthma during early childhood. METHODS We performed a cohort study with 10 440 children whose mothers attended the midwife centres in Odense and Aalborg, Denmark, from April 1984 to April 1987 at approximately the 36th week of gestation. Information on hospitalization with asthma was extracted from the National Hospital Discharge Registry, which allowed a complete follow-up of all members of the cohort who remained alive and residents in the county. RESULTS The cumulative incidence rates of hospitalization with 'definite' and 'any' asthma were 3.5% and 5.0%, respectively, at 12 years of age. After adjusting for potential confounders, there were increased trends in the risk of asthma hospitalization with birthweight and ponderal index. More pronounced trends, particularly in the risk of definite asthma, were found among children of over the average birthweight (IRR = 1.62, 95% CI: 1.02-2.59 per 1000 g increase) or ponderal index (IRR = 1.06, 95% CI: 1.02-1.10 per 0.1 g/cm(3) increase). However, the increased risk in large babies was seen only in children with a ponderal index of > or =2.5 g/cm3. CONCLUSION Birthweight and ponderal index were associated with childhood asthma indicated by hospitalization. Fetal growth itself, determinants of fetal growth, or any unadjusted factors that correlate with fetal growth, could cause the association.