Contrasting associations of maternal smoking and pre-pregnancy BMI with wheeze and eczema in children

Background: Childhood allergies are dynamic and associated with environmental factors. The influence of prenatal maternal smoking and obesity on childhood allergies and their comorbidities remains unclear, especially in prospective cohorts with serial longitudinal observations. Objective: We examined time trends in the prevalence and comorbidity of childhood allergies, including wheeze, eczema, and rhinoconjunctivitis, using a large-scale, population-based birth cohort in Japan, and assessed the effects of prenatal maternal smoking and BMI on the risk of childhood allergies. Methods: Parents completed the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaires about symptoms of allergies and their risk factors at age 1, 2, 4, and 7 years. Complete data from all pre- and postnatal questionnaires at age 1, 2, 4, and 7 were available for 3296 mother–child pairs. Results: We observed significant overlap of childhood allergies at 1, 2, 4, and 7 years. Maternal serum cotinine during pregnancy was associated with increased risk of wheezing in the children at age 1, 2, and 4 but disappeared at age 7. In contrast, maternal cotinine levels were inversely associated with the prevalence of eczema in children at age 7. We additionally observed that maternal pre-pregnancy BMI, not children's BMI, had a positive association with wheeze and an inverse association with eczema in 7-year-old children, respectively. We did not find any association of examined maternal factors and rhinoconjunctivitis. Conclusions: We demonstrated contrasting association of prenatal maternal smoking and high BMI with postnatal wheeze and eczema. For precise assessment of allergy-associated risk factors, we need to contrast risk factors for different allergic diseases since focusing solely on one allergic disease may result in misleading information on the role of different risk factors.