1. Prenatal exposure to air pollutants was associated with detrimental effects on lung function in young children.
2. Results of this study suggest that in utero exposure to air pollutants during the second trimester may be more related to the adverse effects on airway function than postnatal exposure.
Evidence Rating Level: 2 (Good)
Study Rundown: Development of respiratory airways in humans begins during the second and third trimesters of pregnancy and continues until 3 years of age. Studies have suggested that airways may be highly susceptible to permanent damage if the child is exposed to air pollution in utero or postnatally. This study used nitrogen dioxide (NO2) and benzene levels in the air as proxies for pollutant levels related to traffic fumes and industrial activities. Pulmonary effects of prenatal and postnatal pollutant exposure were followed-up in children at the age of 4.5 years by way of lung function tests. It was found that higher prenatal exposure to air pollutants was associated with lower expiratory flow volumes. Exposure during the second trimester of pregnancy held the most significant relationship with diminished lung function.
One of the major limitations of this study stems from the low rate of follow-up. Compared to mothers whose children were excluded from the analysis due to loss to follow-up or improper testing, the mothers of children included in the analysis were older and of higher socioeconomic status. Children included in the final analysis also had higher incidences of wheezing and lower respiratory tract infections in infancy and better day care attendance. While this should not compromise the conclusions of this study, bias effecting the magnitude of the results may have been introduced. Regardless, this is the first prospective, population-based study to assess and demonstrate the association between prenatal air pollution exposure and lung function in children of preschool age.
In-Depth [prospective cohort]: This study, an analysis of data from two locations in the Infancia y Medio Ambiente Project in Spain, examined the effects of prenatal and postnatal exposure to air pollution on lung function in children. Of the 1295 pregnant women who were enrolled in the study at the time of their first antenatal visit, lung function tests from 620 children at 4.5 years of age were included in the final analysis. Air levels of NO2 and benzene were used as proxies for air pollution. For each interquartile range increase in pollutant exposure during the second trimester, forced expiratory volume in one second (FEV1) was decreased by 18.4mL (CI95% -34.8 to -2.1) for benzene and 28.0 mL (CI95% -52.9 to -3.2) for NO2. FEV1 was decreased by 51.9 mL (CI95% -97.9 to -5.9) for every 1 µg/m3 increase in benzene exposure and 17.4 mL (CI95% -32.8 to -2.0) for every 10 µg/m3 increase in NO2 exposure during the second trimester. The risk of having <80% of predicted FEV1 increased with each IQR increase of NO2 and benzene contact during the second trimester (RR, 1.22, CI95% 0.97 to 1.76) and (RR, 1.30 CI95% 1.02 to 1.46) respectively. Although air pollutant contact during the third trimester and first year of life seemed to cause diminished lung function, the findings were not statistically significant.
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