| ObjectivePreterm birth（PTB）is one of the common adverse pregnancy outcomes.Approximately 15 million PTBs are born worldwide every year,which brings a heavy economic and medical burden to the families and society.Given the rapid development of industry and transportation,air pollution has become a key public health problem,and pose serious health threat to human,especially to the pregnancy outcomes of pregnant women.Previous abortion has multiple adverse effects on women’s physiology and psychology health,and plays a key role in the adverse pregnancy outcomes when those women become pregnant again.It remains unclear whether air pollution is related to the risk of PTB among pregnant women with previous abortion,and whether the types and numbers of previous abortion can affect above relationship.Therefore,the current study aims to explore the effect of prenatal air pollution on the risk of PTB among the pregnant women with previous abortion,and the potential modification effect of previous abortion on the above relationship.Our findings could provide a scientific basis for improving population quality and reducing medical burden.Material and method1.Study area and participantsThe baseline information of the participants come from the National Free Preconception Health Examination Project（NFPHEP）in Henan Province.We collected data of pregnant women who live in rural Henan Province and conceived during May 13,2014 and December 31,2016.Based on the inclusion and exclusion criteria,we recruited 57337 pairs of pregnant women with previous abortion and their singleton live births.2.Exposure assessmentWe obtained air pollution data from 75 air pollution monitoring stations in Henan Province and 76 air pollution monitoring stations outside the province within 100kilometers from the border of Henan Province from May 13,2014 to December 31,2017.The data on air pollution include daily average for inhalable particles(PM10),fine particulate matter(PM2.5),nitrogen dioxide（NO2）,sulfur dioxide（SO2）,carbon monoxide（CO）,and an 8-h maximum for ozone（O3）.An inverse distance-weighted model（IDW）was employed to evaluate the air pollution data of counties,which were used to estimate the exposure levels of pregnant women during pregnancy.3.Statistical analysisThe IDW and geographic data visualization were performed using ArcGIS 10.7software.Pearson correlation analysis was used to evaluate the correlation of air pollutants.The chi-square test and t-test was used to examine the difference in participant characteristics between the PTB group and term birth group.The distribution lag nonlinear model（DLNM）was used to explore the relationship between air pollutant exposure during each gestational week and the risk of PTB.Logistic regression model was used to analyze the effect of air pollutant exposure during the whole pregnancy and trimesters on the risk of PTB.Meanwhile,the potential modification effect of previous abortion on the above relationships was explored using an interaction analysis.All statistical analyses are based on R software.A P<0.05 for a two-side test was considered statistically.Results1.Demographic characteristics of participantsOf 57337 pregnant women with previous abortion and their singleton live births,1975 of them were PTBs（3.44%）.Before this live birth,14.56%（n=8349）,83.23%（n=47722）and 2.21%（n=1266）of pregnant women had experienced only spontaneous abortion,only induced abortion,and both spontaneous and induced abortion,respectively.The proportion of pregnant women had 1,2 or>2 abortions were80.97%（n=46424）,15.93%（n=9136）and 3.10%（n=1777）,respectively.2.Descriptive analysis of air pollution in Henan Province from 2014 to 2017The concentration of PM10,PM2.5,NO2,SO2,CO,and O3during 2014 and 2017in Henan Province were 125.57±60.13μg/m3,72.39±43.61μg/m3,40.86±14.56μg/m3,32.28±19.06μg/m3,1.41±0.52 mg/m3 and 98.42±44.52μg/m3,respectively.Except for O3,the concentration of the other five air pollutants were higher in winter,while the concentration of O3 was higher in spring and summer.3.Sensitive exposure window of pregnant women with previous abortion to air pollutionAccording to the results based on the DLNM,the strongest associations with the risk of PTB were observed in 36th week for PM10,23rd week for PM2.5,10th(or 11th)week for NO2,13th week for SO2 and 31st week for CO during pregnancy.Pregnant women with previous abortion are more sensitive to air pollution during the early and late stages of pregnancy.4.Association between air pollution during pregnancy and the risk of PTB among pregnant women with previous abortionAfter adjusting the covariates,it was showed that the risk of PTB of pregnant women with previous abortion was significantly associated with the NO2,SO2,CO and O3 exposure during pregnancy（P<0.05）.There was no significant correlation between the risk of PTB and PM2.5 or PM10 exposure during pregnancy or trimesters（P>0.05）.With each 10μg/m3 increase in NO2 and SO2 exposure during the entire pregnancy,the risk of PTB increased by 31.9%[Odds ratio（OR）:1.319,95%Confidence interval（CI）:1.226,1.418]and 54.1%（OR:1.541,95%CI:1.237,1.920）,respectively.For each 1.0mg/m3 increase in CO exposure in the third trimester of pregnancy,the OR of the risk of PTB was 1.142（95%CI:1.013,1.287）.Additionally,we found that with each 10μg/m3 increase in O3 exposure during the entire pregnancy,the risk of PTB decreased by 23.3%（OR:0.767,95%CI:0.732,0.804）.5.Modification effect of previous abortion on the association between air pollution and PTB riskThe type of previous abortion could significantly modify the effect of air pollution on the risk of PTB(P-interaction<0.05).Compared with pregnant women with only induced abortion,pregnant women with only spontaneous abortion were more sensitive to NO2（during the entire pregnancy and first trimester of pregnancy）,CO（during the first trimester）,and O3（during the entire pregnancy）.However,we did not observe a significant modifying effect of the number of previous abortions on the relationship between air pollution and the risk of PTB(P-interaction>0.05).Conclusions1.Exposure to PM10,PM2.5,NO2,SO2 and CO during pregnancy can increase the risk of PTB among pregnant women with previous abortion,while at the level of air pollution exposure in this study,the risk of PTB was decreased with the increased O3exposure.The air pollution exposure in the early and late pregnancy are more likely to trigger PTB.2.The type of previous abortion can modify the association between air pollution and the risk of PTB.Compared with pregnant women with only induced abortion,pregnant women with only spontaneous abortion are more sensitive to air pollution exposure during pregnancy. |
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