Low Birth Weight and Asthma in Young Adults from a Brazilian Birth Cohort

Background: According to the hypothesis of the Developmental Origin of Health and Disease, scientific evidence suggest that adverse intrauterine conditions impair fetal growth and may have long-term consequences facilitating development of chronic noncommunicable diseases in adulthood. These adverse conditions, such as low birth weight (LBW) have been identify as risk factors for asthma.

Aims: Evaluate the association between LBW and the development of asthma in young adult.

Methods: Brazilian cohort study (1978/79) including 1815 young adults aged 23 to 25 years old. Standardized questionnaires and methacholine bronchoprovocative were employed. Outcome variable was asthma and exposure variable LBW. A directed acyclic graph (DAG) was design to map cause and effect relationships between variables analyzed; three constructs were create: asthma, birth economic status (Birth SES) and current economic status (Current SES). Asthma construct was set up for bronchial hyperreactivity (PCO2 value ≤ 4mg/ml), wheezing in the last 12 months and medical diagnosis of asthma. Associations were obtained by Structural Equations Model (SEM), analyzing the direct and indirect ways.

Results: 13.9% were diagnose with asthma. There was no direct association between LBW with asthma in adulthood (total effect: CP = 0.116, p = 0.184; direct effect: CP = 0.092, p = 0.540). However four indirect pathways were observed between LBW and adult asthma: 1) SES current via adult smoking (CP = 0.019; p = 0.020); 2) birth SES via current SES and adult smoking (CP = -0.004; p = 0.044); 3) maternal age via maternal smoking, BPN, current SES and adult smoking (CP = -0.001; p = 0.049); 4) maternal smoking via BPN, current SES and adult smoking (CP = 0.006, p = 0.031).

Conclusion: In this cohort, low birth weight did not increase the direct risk of asthma in young adults, but was indirectly associated with asthma via socioeconomic and maternal variables.