Gestational age at birth and risk of allergic rhinitis in young adulthood

BackgroundPrevious studies of the association between gestational age or birth weight and allergic rhinitis in later life have had various limitations, including the inability to estimate risk among subjects born extremely preterm or to examine specific contributions of gestational age and fetal growth.ObjectiveWe sought to determine whether gestational age at birth independent of fetal growth is associated with allergic rhinitis medication prescription in a national cohort of young adults.MethodsWe conducted a national cohort study of 630,090 infants born in Sweden from 1973 through 1979 including 27,953 born preterm (<37 weeks) and followed for prescription of nasal corticosteroids and oral antihistamines in 2005-2009 (age, 25.5-37.0 years). Medication data were obtained from all outpatient and inpatient pharmacies throughout Sweden.ResultsThe overall prevalence of nasal corticosteroid and oral antihistamine prescription was 16.3% and 16.8%, respectively, which is similar to the reported prevalence of allergic rhinitis in this population. Low gestational age at birth was associated with a decreased risk of nasal corticosteroid and oral antihistamine prescription in young adulthood after adjusting for fetal growth and other potential confounders. For subjects born extremely preterm (23-28 weeks), adjusted odds ratios were 0.70 (95% CI, 0.51-0.96) for nasal corticosteroid prescription and 0.45 (95% CI, 0.27-0.76) for both nasal corticosteroid and oral antihistamine prescription relative to those born at full term.ConclusionThese findings suggest that low gestational age at birth independent of fetal growth is associated with a decreased risk of allergic rhinitis in young adulthood, possibly because of a protective effect of earlier exposure to pathogens.