AIMS

Various different asthma definitions are used in research and clinic. It is important to identify specific underlying mechanisms for the associations of early life exposures with different asthma related outcomes, which might reflect different specific structural and functional adaptations. Major potential early life risk factors are a low birth weight, and change in infant's growth. In a large population-based cohort study followed from birth until the age of 17 years, our aim is to identify potential risk factors for the different asthma phenotypes in young adulthood.

HYPOTHESIS

A recent paper on fetal and infant growth and asthma symptoms in preschool children showed an association between infant weight gain and asthma symptoms, independent of fetal growth, suggesting that early infancy might be critical for the development of asthma. The effect of infant growth on asthma phenotypes and lung function measurements at older ages needs to be explored. If adverse infant growth is also associated with respiratory outcomes in young adulthood, a valuable and modifiable risk factor is identified which could be potentially used for new preventive, diagnostic and therapeutic approaches.

Low birth weight is associated with increased risks of asthma, chronic obstructive lung disease, and impaired lung function in adults and with increased risks of respiratory symptoms in the first 7 years. Low birth weight per se is not likely to be the causal factor for asthma. The same birth weight might be the result of various growth patterns. The developmental plasticity hypothesis suggests that the associations between low birth weight and diseases in later life are explained by early adaptation mechanisms in response to various adverse exposures, including smoke exposure. Previous studies showed inconclusive results about fetal growth patterns and fetal smoke exposure and the risk of wheezing in childhood. The associations of longitudinally measured fetal and early childhood growth patterns, and their interactions with wheezing phenotypes, asthma, bronchial hyperresponsiveness and lung function in later life need to be studied in detail.

EXPOSURE VARIABLES

Birth weight and infant growth.

POTENTIAL CONFOUNDER VARIABLES

parental age, body mass index, education and occupation, history of asthma or atopy, smoking during pregancy, gestational age at birth, children's gender, crowding, siblings, breastfeeding status, ethnicity, tobacco smoke exposure, housing, pet keeping and body mass index at time of outcome.

OUTCOME VARIABLES

(1) recently identified asthma phenotypes: never/infrequent wheeze, transient early wheeze, prolonged early wheeze, intermediate onset wheeze, late onset wheeze, persistent wheeze; (2) doctor diagnosed asthma; at ages 8 and 15 years (2) Lung function (spirometry, bronchial responsiveness to methacholine, exhaled nitric oxide; at ages 8 and 15 years).