Pollen exposure in pregnancy and infancy and risk of childhood asthma

Abstract

Aims and Objective: Reported associations between season of birth and childhood asthma may be related to pollen exposure. We aimed to estimate the association between airborne allergenic pollen concentration in pregnancy or infancy and subsequent asthma in a population-based setting. Methods: Two cohorts identified from the Swedish Medical Birth register were linked to national health registers. We estimated the association between exposure to airborne pollen of birch or alder + hazel and asthma incidence by Cox regression (cohort born 2005-2010, n=80 587) and current asthma in the 6th year of life with logistic regression (cohort born 2001-2004, n=38 059). Results: In both cohorts, higher pollen exposure in pregnancy showed mostly null or negative associations with childhood asthma, while higher exposure in infancy showed null or positive associations (Figure 1). Exposure to alder and hazel pollen in infancy seemed to be more important for asthma incidence, while birch pollen seemed more important for current asthma in the 6th year of life. Conclusion: Exposure to high pollen levels in infancy may be a risk factor for asthma, while high levels in pregnancy may be protective.