[Relationship between exposure to air pollutants during pre-pregnancy or early pregnancy and birth defects in Xi'an, 2013-2015: a case crossover study].

Objective: To understand the levels of exposure to traffic-related air pollutants including nitrogen dioxide (NO(2)), PM(10) and PM(2.5), and the relationship between the exposure to air pollutants during pre-pregnancy or early pregnancy and birth defects. Methods: Data on air pollution and birth defects from 2013 to 2015 was collected. A case-crossover design was employed to analyze the exposure-response relationship between traffic-related air pollutants and birth defects. Results: A total of 4 235 pregnant women were studied. During the study period, the daily average concentrations of ambient NO(2), PM(10) and PM(2.5) appeared as 60.83 µg/m(3), 104.94 µg/m(3) and 103.88 µg/m(3), respectively, with the concentration of PM(2.5) larger than the 2(nd) version of Standard National Ambient Air Quality Standard. In addition, there were strong correlations seen between each of the pollutants (P<0.01). After adjustment for the influence of meteorological factors, it was found that the exposure to high level of NO(2) and PM(10) during pre-pregnancy or early pregnancy increased the risk on birth defects (P<0.05). Conclusion: Levels of exposure to adverse environmental factors during pre- pregnancy or early pregnancy could increase the risk of birth defects, suggesting that in these sensitive periods, women should try to avoid being exposed to high concentration of traffic-related air pollutants as NO(2), PM(10) etc. in order to reduce the risk of birth defects.