Perinatal factors influencing the development of childhood asthma
Perinatal risk factors are suspected to have a significant impact on the development of asthma; however, their role in the development of this disease is not firmly established.
Asthma is a serious health problem worldwide. There are approximately 334 million patients with asthma globally, and its prevalence ranges from 1% to 16%. Further, asthma is the most common chronic disease in children, and the prevalence of childhood asthma has increased during the past 30 years. Asthma is caused by a combination of genetic predisposition and environmental factors. Although there is clear evidence that genetic predisposition contributes to the development of asthma, the rapid increase in its prevalence during the past 30 years suggests that environmental factors play a more crucial role. Previously known environmental risk factors for asthma development include environmental tobacco smoke, air pollution, Westernized living conditions, dietary habits, allergen exposure, obesity, pet breeding, and the use of antibiotics in the first year of life. To date, however, most studies evaluating risk factors for the development of asthma have been limited to life events occurring long after birth. Fortunately, active research is investigating various environmental risk factors for asthma development that are present in utero or during the perinatal period. The role of perinatal risk factors in the development of asthma is not firmly established. Although preterm birth, low birth weight, cesarean section, general anesthesia, respiratory distress syndrome, transient tachypnea of the newborn, and meconium aspiration syndrome have been associated with the development of asthma, the number of studies is small and in some factors the results are inconsistent; therefore, further researches are needed. Recently, interesting studies investigating synergistic mechanisms of perinatal factors in the development of asthma have been published. According to these studies, perinatal factors alone have little to no impact on the development of asthma or confer only a slight increase in risk. However, in the presence of associated risk factors, such as prematurity plus chorioamnionitis, prematurity plus atopy, or prematurity plus maternal smoking during pregnancy, the risk for asthma dramatically increases. In other words, perinatal factors alone (eg, prematurity) are not significant risk factors for asthma development. However, simultaneous exposure to other risk factors (eg, atopy) could affect asthma development. With these considerations, Kim A et al have hypothesized that perinatal factors would be associated with the development of asthma; however, this association would depend on exposure to other risk factors. The objective of their study was to evaluate whether perinatal factors and other risk factors have an independent or combined effect on the development of asthma. This study involved 3770 children (mean age 9.1 years, range 5.68-12.16 years; 51.9% boys) who were enrolled in the Elementary School Student Cohort (2009-2014) in Ulsan University Hospital (Ulsan, Korea). Subjects were divided into an asthma group (n = 514) and a non-asthma group (n = 3256). Multivariate analyses showed that early life (within first week) oxygen therapy (adjusted odds ratio [aOR] 1.864, 95% confidence interval [CI] 1.156-3.004) and breastfeeding (aOR 0.763, 95% CI 0.606-0.960) were 2 significant perinatal factors influencing the development of asthma. Environmental tobacco smoke (aOR 1.634, 95% CI 1.298-2.058) and parental allergic disease (aOR 1.882, 95% CI 1.521-2.328) also were identified as risk factors. Using subgroup analyses, combined effects on asthma development were observed between perinatal factors (early life oxygen therapy and breastfeeding) and other risk factors (vicinity to major roadway [traffic-related air pollution], environmental tobacco smoke, parental allergic disease, and atopy). The authors concuded that early life oxygen therapy and breastfeeding were important perinatal factors influencing the development of asthma; early life oxygen therapy would be an important perinatal factor influencing the development of asthma, in contrast, breastfeeding was identified as having a significant protective effect against asthma development. Furthermore, Kim A et al have demonstrated that these perinatal factors have combined effects with other risk factors, including environmental tobacco smoke, traffic-related air pollution, parental allergic disease, and atopy on the development of asthma.