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Wang, Q, Benmarhnia T, Li CC, Knibbs LD, Bao JZ, Ren M, Zhang HH, Wang SH, Zhang YW, Zhao QG, Huang CR.  2019.  Seasonal analyses of the association between prenatal ambient air pollution exposure and birth weight for gestational age in Guangzhou, China. Science of the Total Environment. 649:526-534.   10.1016/j.scitotenv.2018.08.303   AbstractWebsite

Ambient air pollution has been linked to small for gestational age (SGA); however, the relationship with large for gestational age (ILA) is unclear and very few studies have investigated seasonal effects on the association between air pollution and SGA or LGA. Using birth registry data of 506,000 singleton live births from 11 districts in Guangzhou, China between January 2015 and July 2017, we examined associations between ambient air pollutants (PM2.5, PM10, NO2, SO2, and O-3) and SGA/LGA, and further assessed the modification effect of season. Daily concentrations of air pollutants from 11 monitoring stations were used to estimate district-specific exposures for each participant based on their district of residence during pregnancy. Two-level binary logistic regression models were used to evaluate associations between air pollution and SGA/LGA. Stratified analyses by season and a Cochran Q test were performed to assess the modification of season. Exposure to PM2.5, NO2, SO2, and O-3 was significantly associated with increased risk of SGA, especially for exposure during the second and trimester. For an interquartile range (IQR) increase in PM2.5(6.5 mu g/m(3)), NO2 (12.7 mu g/m(3)), SO2 (2.8 mu g/m(3)) and O-3 (20.8 mu g/m(3)) during the entire pregnancy, SGA risk increased by 2% (OR - 1.02, 95% CI: 1.00-1.04), 8% (OR = 1.08, 95% CI: 1.04-1.12), 2% (OR - 1.02, 95% CI: 1.01-1.03), and 14% (1.14, 1.11-1.17), respectively. A decreased risk of WA was found for PM2.5, PM10, SO2, and O-3 during the first trimester or entire pregnancy. When examined by season, significant associations between air pollutants and SGA were observed for women who conceived during summer or fall, and the patterns were consistent for all pollutants. Our study suggests that conception during different seasons might modify the association between ambient air pollution and SGA. (C) 2018 Elsevier B.V. All rights reserved.

Benmarhnia, T, Auger N, Stanislas V, Lo E, Kaufman JS.  2015.  The relationship between apparent temperature and daily number of live births in Montreal. Maternal and Child Health Journal. 19:2548-2551.   10.1007/s10995-015-1794-y   AbstractWebsite

Temperature is a hypothesized determinant of early delivery, but seasonal and long term trends, delayed effects of temperature, and the influence of extreme cold temperatures have not yet been addressed. We aim to study the influence of apparent temperature on daily number of births, considering lag structures, seasonality and long term trends.We used daily number of births in conjunction with apparent outdoor temperatures between 1981 and 2010 in Montreal. We used Poisson regression combined with a distributed lag nonlinear model to consider non-linear relationships between temperature and daily number of births across specific lag periods.We found that apparent temperature was associated with the daily number of births in Montreal, with a 1-day delay. We found an increase in births on hot days, and decrease on cold days, both offset by a harvesting effect after 4 and 5 days.This study suggests that the number of births is affected by extreme temperatures. Obstetric and perinatal service providers should be prepared for spikes in the number of births caused by extreme temperatures.