Effect Of Air Pollution And Ambient Temperature On Preterm Birth In The Pearl River Delta Region,China

Background:Preterm birth(PTB)is the major cause of deaths in children under five years old,and is closely related to adult diseases.Studies have reported that exposure to air pollution and temperature extremes during pregnancy increases the risk of preterm birth.The Pearl River Delta(PRD)is a major industrial region in China,with a large emission of pollutants,a large number of immigrants and unclear reasons for high incidence of premature delivery.In addition,the PRD is located in the subtropical oceanic monsoon climate zone,hit by an unusually persistent and widespread severe cold spell in 2008.Given global concerns about increasing air pollution and extreme weather,there is an urgent need to determine the effect of air pollution and ambient temperature on preterm birth.Objectives:(1)To investigate the effect of maternal air pollution exposure during pregnancy on PTB,and to differentiate the effect between local residents and migrants in PRD.(2)To study the effect of cold and heat exposure during pregnancy on PTB,and to determine the effect size varying by the trimester and pregnant women subgroup.(3)To examine the effect of 2008 cold spell exposure on PTB.Methods:(1)We established a birth cohort with a total of 628,439 mother-and-live-birth pairs in seven major cities of PRD during 2015-2017.The mothers were included in the cohort at their first time hospital visit for pregnancy,and then followed up until the born of the baby.The air pollution exposure was estimated based on the daily air pollution concentrations in the nearby air monitors and the pregnancy period.Cox proportional hazards models were utilized to estimate the associations between each air pollutant and PTB at different pregnancy periods for local residents and migrants.(2)The cold and heat exposure was estimated based on the daily ambient temperature and the pregnancy period.Cox proportional hazards models were utilized to estimate the associations between cold and heat exposure and PTB at different pregnancy periods,by controlling maternal age,infant sex,pregnancy history,air pollutants and relative humidity.(3)Data of daily preterm birth,air pollution and meteorological variables from 2006 to 2010 were collected in Dongguan and Shenzhen.A Poisson regression with a distributed lag nonlinear model was used to investigate the association between the 2008 cold spell and daily premature for each city.Results:(1)Our cohort included a total of 628,439 mothers.Among them,308,201 women were local residents,and 320,238 women were migrants.We observed stronger effects among the migrants than local residents.For the exposure during the entire pregnancy,the hazard ratio(HR)among the migrants was 1.564(95%CI:1.496,1.634)for each 10 ?g/m3 increase in PM2.5,1.151(95%CI:1.125,1.177)for each 10 ?g/m3 increase in O3,and 1.479(95%CI:1.395,1.568)for each 10 ?g/m3 increase in SO2.(2)Our cohort included a total of 628,439 live births.Among them,29,849 were preterm births,accounting for 4.75%of the total live births.For the adjusted model,the strongest effect of cold exposure on PTB were observed during trimester 3,with HR 1.647(95%CI:1.560,1.739),respectively,as well as the strongest effect of heat exposure on PTB were observed during trimester 3,with HR 1.428(95%CI:1.365,1.494),respectively.(3)During the 2008 cold spell,total preterm births were increased by 22.44%and 21.25%in Dongguan and Shenzhen,respectively.The effect of the cold spell on preterm births lasted for over one week,the lag0-6 days cumulative relative risk(RR)is 1.317(95%CI:1.101,1.576)and 1.405(95%CI:1.177,1.676)in Dongguan and Shenzhen,respectively.The effects were found to be more pronounced for the pregnant women with 35?36 gestation weeks and maternal age<35 years group.Conclusions:(1)Maternal PM2.5,O3 and SO2 exposure might be important risk factors of preterm birth,particularly among the migrants in PRD.More specific protective and education measures should be considered for the migrant pregnant women.(2)Maternal cold and heat exposure might be one important risk factor of PTB,especially for women at late stage of pregnancy in PRD.Maternal age ?35 year pregnant women might be the vulnerable subgroup.(3)Cold spell could increase the risk of preterm births in Dongguan and Shenzhen,and the effect lasts for over one week.Specific measures should be considered to protect the pregnant women,especially the vulnerable subgroups.