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Background Exposure to ambient nitrogen dioxide (NO2) could increase the risks of small for gestational age (SGA) and large for gestational age (LGA). Nevertheless, previous published studies usually use a time period over relatively long durations as the exposure window, such as trimester-specific or gestational months, to identify adverse pregnancy outcomes related susceptible exposure windows for ambient air pollution. At present, no study has explored associations of weekly-specific ambient air NO2 exposure around pregnancy with SGA and LGA. Objective To evaluate the associations of exposure to ambient NO2 over the preconception and entire pregnancy period with risks of SGA and LGA, as well as to explore critical windows of NO2 exposure by refining exposure period to specific weeks. Methods Based on a birth cohort established by the project Environmental and LifEstyle FActors iN metabolic health throughout life-course Trajectories (ELEFANT) situated in Tianjin, 10 916 singleton pregnant women whose dates of the last menstrual period and delivery were both between June 2014 and June 2016, and whose gestational age were within 24-42 completed gestational weeks were included in this study. Each pregnant woman's exposures to ambient NO2 throughout 12 weeks before pregnancy and pregnancy period were matched with daily average NO2 concentrations obtained from the Chinese air quality reanalysis datasets (CAQRA). Distributed lag models incorporated in Cox proportional hazard regression models were applied to explore the associations of maternal exposure to weekly ambient NO2 throughout 12 weeks before pregnancy and pregnancy period with risks of SGA and LGA after controlling for potential confounders including maternal age, ethnicity, educational level, occupation, body mass index before pregnancy, residence, times of gravidity and parity, smoking, alcohol consumption, husband smoking, and season of conception. Hazard ratios (HRs) with 95% confidence intervals (CIs) were calculated per 3 μg·m−3 increase in ambient NO2 concentrations. Results The average levels of maternal exposure to NO2 over the preconception, first trimester, second trimester, third trimester, and entire pregnancy periods were (39.6±10.8), (42.7±10.5), (44.8±12.7), (37.7±11.1), and (41.6±4.8) μg·m−3, respectively. For a 3 μg·m−3 increase in NO2 over the first trimester, the risk of SGA increased by 19.0% (95%CI: 8.0%-32.0%). For a 3 μg·m−3 increase in NO2 over the preconception, first trimester, and entire pregnancy, the associated risks of LGA increased by 7.0% (95%CI: 1.0%-13.0%), 37.0% (95%CI: 29.0%-46.0%) and 19.0% (95%CI: 9.0%-31.0%), respectively. For SGA, the susceptible exposure windows for NO2 were observed during the 7th to 12th preconceptional weeks and the 6th to 12th gestational weeks, with the strongest association found at the 12th preconceptional week, when the risk of SGA increased by 6.0% (95%CI:3.2%-8.9%) for a 3 μg·m−3 increase in NO2. For LGA, the susceptible exposure windows for NO2 were observed during the 1st to 12th preconceptional weeks and the 1st to 6th gestational weeks, with the strongest association found at the 12th preconceptional week, when the risk of LGA increased by 6.1% (95%CI: 4.5%-7.8%) for a 3 μg·m−3 increase in NO2. Conclusion Exposure to ambient NO2 is associated with increased risks of both SGA and LGA, and the most susceptible weekly exposure windows are nested within the 12 weeks before pregnancy and early pregnancy.
RESUMO
Objective@#To evaluate the effects of exposure to ozone (O3) on sperm quality during different stages of spermatogenesis.@*Methods@#All 1 780 subjects attending to the Reproductive Medicine Center in Renmin Hospital of Wuhan University were recruited from April, 4, 2013 to June, 30, 2015. The subjects were living in Wuhan more than 3 months before attending to the program, aged 20 to 40 years. Semen quality (sperm concentration and sperm count) were measured according to standardized protocols. Corresponding daily 8 hours average concentration of O3, other polluted concentration, average temperature and relative humidity were collected in different time, including lag 0, 10, 70 and 90 d, and lag 0-9 d, lag 10-14 d, lag 70-90 d and lag 0-90 d. After controlling the age, BMI, education level and other confounders, generalized linear Model was used to investigate the association between O3 and sperm quality during different stages of spermatogenesis.@*Results@#Average daily concentration of O3 during the study period was (114.20±74.88) μg/m3 and the mean values of sperm concentration and count were (76.32±50.17) millions/ml and (164.77 ± 133.05) millions/sample, respectively. Exposure to O3 was associated with decreasing sperm concentration and count. For every 1 μg/m3 increase of O3, the decrease of sperm concentration during lag 10, lag 0-9 and lag 10-14 days exposure windows were 0.040 (95%CI: 0.004-0.077) millions/ml, 0.081 (95% CI: 0.003-0.158) millions/ml and 0.059 (95% CI: 0.001-0.116) millions/ml, respectively. And the decrease of sperm count during lag 10, lag 0-9 days exposure windows were 0.105 (95%CI: 0.008-0.202) millions/sample and 0.221 (95% CI: 0.016-0.426) millions/sample. After stratification, in the ozone concentration <P50 and ≥P50 groups, and the number of subjects in each exposure windows (lag 0-9, lag 10-14, lag 70-90, lag 0-90 days) were 887 and 893, 890 and 890, 895 and 885, 889 and 891, respectively. Compared with the high ozone concentration group, the effects of low group were more obvious. Furthermore, the effects of low concentration group was the most obvious during lag 10-14 days, for every 1 μg/m3 increase of O3, the decrease of sperm concentration was 0.249 (95% CI: 0.028-0.470) millions/ml. After sensitivity analysis, the effects of exposure to ozone on sperm concentration and sperm count remained relatively unchanged.@*Conclusion@#Our study suggested that exposure to O3 was significantly associated with decreasing semen quality in Wuhan. Moreover, the effects were more obvious during lag 0-9 and lag 10-14 days.