Birth Cohort Studies on Asthma Development

In past decades the prevalence of asthma in children has increased substantially but this trend seems not to have persisted into the twenty-first century. What might have caused the increased prevalence is not well understood. With the expectation that the prevalence may be decreased by reducing exposure to environmental factors, several birth cohort studies are being (or have been) carried out all over the world. Although many studies are still ongoing, decisions on data gathered by these studies will be of great importance for clinical practice. An overview of designs of available studies will be essential in constructing a metaanalysis. We describe the similarities and differences between designs and variable sets of birth cohort studies focusing on the relationship between allergen exposure (solely or in combination with other environmental exposures) and development of childhood asthma. We also evaluate which studies are particularly qualified for inclusion in a meta-analysis relating asthma preventi...