Effects Of Atmospheric Temperature Fluctuation On The Risk Of Rural Preterm Birth In Henan

ObjectivePreterm birth(PTB)is a common adverse pregnancy outcome.Although the economic and medical level has improved,the incidence of PTB has not decreased significantly.The global incidence of PTB is still as high as 10.2%in 2013.More and more studies have paid attention to the relationship between environmental factors and the risk of PTB.In recent years,the global temperature is rising at the rate of 0.1??0.2?for each 10 years.The frequency and intensity for extreme weather are increasing,which has a huge impact on the health of the population,especially for pregnant women.Increasing studies on the effects of atmospheric temperature were mostly conducted urban areas,but less attention was paid to on the rural areas.Henan Province is a large agricultural province in our country with a large rural population.The rural population was about 50 million from 2013 to 2016.The significant difference between urban and rural areas are observed.Therefore,it is more effective to focus on the relationship between the change of atmospheric temperature and the risk of PTB in rural areas and the influencing factors,so as to prevent the occurrence of PTB in rural areas.This study is aimed to explore the association between atmospheric temperature and the risk of PTB,in order to clarify the exact exposure windows of the effects of ambient temperature on PTB and screen the high-risk population.Our findings may provide targeted prevention and treatment measures to reduce the incidence of PTB in rural areas.Materials and methods1.Study areaHenan Province is located in the central areas with warm temperate of China,and its climate is complex and volatile.In addition,Henan Province,a large agricultural province,has a great number of populations,especially rural population.From 2013 to2016,the rural population of Henan Province is 50 million.2.Data collection and preprocessingThe study is based on the National Free Preconception Health Examination Project,and the demographic characteristic and pregnancy outcomes of pregnant women and newborns were collected from self-reported interviews,preconception physical examinations,early pregnancy follow-up and postpartum follow-up.According the inclusion and exclusion criteria,1232987 singleton live birth were finally included.We obtained the meteorological data including daily mean atmospheric temperature,maximum atmospheric temperature,minimum atmospheric temperature and relative humidity from the China Meteorological Data Sharing Service System,which covers 15 national meteorological stations in Henan during 2013?2017.We used the Baidu Map pickup coordinate system tool to extract the coordinates of the People's Government of each county.We performed the inverse-distance-weighted(IDW)model to assess individual exposure of meteorological conditions to represent all local participants of each county.Then,the mean atmospheric temperature and relative humidity of each gestational week and each trimester for each participant were calculated by daily meteorological data.3.Statistical analysisThe Arc GIS 10.7 was performed to conduct IDW model and visualize the geographical distribution of mean temperature and PTB.The"mgcv"and"DLNM"software packages in R software were used to establish logistic regression model and distributed lag nonlinear model(DLNM),respectively.The entire pregnancy was divided into first trimester,second trimester,and third trimester,logistic regression model was used to evaluate the association between mean atmospheric temperature change and the risk of PTB.And we also analyzed the effects of heat waves during one week before delivery on the risk of PTB.The DLNM was used to analyze the relationship of temperature exposure,gestational age,and the risk of PTB and evaluate the effects of exposure to extreme temperature on the risk of PTB.The two-sided test level of the interaction in the statistical analysis was?=0.10,and the rest was?=0.05.Results1.Descriptive analysis of meteorological factors in Henan Province during2013?2017 and during the pregnancy for each pregnant womanThe range of mean atmospheric temperature in Henan Province from 2013 to 2017is–7.8??34.5?,showing a significant seasonal fluctuation.The high temperature was concentrated in July and August,and the low temperature in December and January.The ambient mean temperature during the entire pregnancy and first,second and third trimester were 15.77?,16.44?,16.15?,and 14.69?,respectively.2.Demographic characteristics of study population in rural HenanThe number of newborns is 1232987 during 2013?2016 in rural Henan,of them,the proportion of PTB is 2.7%(n=35198).Mothers who were young,more or less BMI,higher school or above,multi-parity,smoking,and drinking are more likely to give birth to PTB infants(P<0.05).Preterm infants account for a large proportion of male infants.3.The temporal and spatial distribution of premature birth rate in rural HenanFrom 2013 to 2016,the incidence of PTB in rural Henan showed a downward trend.The rate of PTB in 2013 is 3.7%and decreased to 2.3%in 2017.The incidence of PTB in the northwest of Henan Province is higher than that in the southeast.The three regions with the highest incidence of preterm birth from 2013 to 2016 are all located in the northwest:Jiaozuo(6.78%),Jiyuan(5.70%)and Zhengzhou(5.52%).4.Association between mean atmospheric temperature change and the risk of PTBThe results of logistic model observed that the risk of PTB during the entire pregnancy increased 13.5%with the 1?increment of atmospheric temperature(OR:1.135,95%CI:1.128?1.142,P<0.001).The significantly positive associations between atmospheric temperature and PTB were only observed in the first trimester and the third trimester(P<0.001).In addition,rural women who were young,overweight,high school and above,multi-parity,and smoking appeared to be more sensitive to the association between the change of atmospheric temperature and the risk of PTB(P_-interaction<0.10).5.Association between exposure to extreme temperature and the risk of PTBDLNM model showed that the association among ambient temperature exposure,gestational age,and the risk of PTB is nonlinear.Compared to the median of mean temperature(P₅₀:14.69?),women exposed to extreme high temperature had the largest effects on the incidence of preterm birth at 36^th weeks of gestation(OR:1.634;95%CI:1.481,1.802),extreme cold at 4^th weeks of gestation(OR:1.484;95%CI:1.109,1.985).Compared to median of mean temperature,the risk of PTB was increased with the increment of ambient temperature in the early pregnancy(weeks 5^th?16^th)and late pregnancy(weeks 32^th?36^th).6.Association between exposure to heat wave during one week before delivery and the risk of PTBExcept for P₇₅-D₂ and P₇₅-D₃,exposure to heat wave was associated with a higher risk of PTB(P<0.05).And the risk of PTB increased with higher temperature thresholds or longer durations.Conclusions1.The risk of PTB is positively associated with the increment of atmospheric temperature.The 5^th?16^th gestational weeks and 32^th?36^th gestational weeks were identified as the susceptible exposure windows for pregnancy women who were exposed to extreme heat during pregnancy and the effects peaked at the 36th gestational weeks.In addition,the risk of PTB increased with intensity of heat wave during one week before delivery.2.The associations between the change of atmospheric temperature and the risk of PTB was stronger among mothers who were young,overweight,higher school or above,multi-parity,and smoking.