Effects Of Ambient Temperature And Humidity Exposure During Pregnancy On The Risk Of Term Low Birth Weight In Offspring

BackgroundIn the context of climate change and frequent extreme weather,adverse health problems caused by temperature and humidity have become severe public health problems.A large number of epidemiological evidence shows that inappropriate ambient temperature and humidity may lead to cardiovascular diseases,respiratory diseases and higher mortality,and adverse health outcomes.Low birth weight(LBW)is one of the commonly reported adverse pregnancy outcomes,which is closely related to the occurrence and development of diseases in childhood and adulthood.Among the many risk factors affecting low birth weight,the exposure of adverse environmental factors during pregnancy is a research hotspot of scholars at home and abroad in recent years.Based on the existing research,the research results for the effect of ambient temperature during pregnancy on the risk of LBW are inconsistent,and there is limited evidence for the association between humidity during pregnancy and LBW.In addition,ambient humidity and temperature jointly affect the body’s heat regulation function.Whereas little is known about the interaction of ambient temperature and humidity on LBW.The characteristics of embryonic development are different in different stages of pregnancy.If the exposure to ambient temperature and humidity is related to the risk of low birth weight,the effects of exposure in different stages of pregnancy may be different.Therefore,it is necessary to identify the critical window period of exposure,which contributes to a scientific basis for further understanding the mechanism of adverse ambient temperature and humidity on embryonic development.ObjectivesThis study aims to explore the relationship between ambient temperature and humidity exposure during pregnancy and the risk of term LBW,analyze the interaction of temperature and humidity on term LBW,and identify the critical window period.In addition,the study also investigates the modification effect of different population characteristics on the effect of temperature and humidity during pregnancy on term LBW and determined the sensitive population.The results can provide a theoretical basis for the prevention of LBW.MethodsThis study is a retrospective epidemiological study.The subjects of the study were mothers who delivered at one month and their infants who were born at one month.According to the purpose of the study,the inclusion and exclusion criteria were formulated.The study population originated in the baseline population of the birth cohort constructed by the research on the incidence mode of asthma in children caused by combined air pollution.From January 2018 to December 2019,subjects were recruited from 15 vaccination clinics in Jinan City,Shandong Province,and the relevant information of parturient women and their offspring was obtained through a face-to-face questionnaire survey.The study outcome was term low birth weight(TLBW)in offspring,which was defined as birth weight<2500g within 37 to 42 weeks of pregnancy.The evaluation indexes of ambient temperature and humidity were the temperature and relative humidity in meteorological data.The daily average data of the Jinan monitoring station from January 2017 to December 2019 were collected.According to the start and end time of pregnancy of each research subject,the individualized temperature and humidity exposure during pregnancy exposure were calculated.General statistical analysis was used for statistical description.The continuous variables that met the normal distribution were described by mean±standard deviation,and the continuous variables that did not meet the normal distribution were described by median and interquartile interval(IQR).The classified variables were expressed by count value(n)and percentage(%).The characteristic differences were compared by independent sample t-test,Wilcoxon rank-sum test,analysis of variance,Kruskal Wallis test,Chi-square test,or Fisher exact test.Inspection standard α=0.05.R 3.4.0 was used for statistical analysis.The generalized additive model(GAM)was used to explore whether there was a linear relationship between ambient temperature and humidity during pregnancy and TLBW.If it is a nonlinear correlation,the independent variables were grouped.The logistic regression model was used to evaluate the effect of different levels of ambient temperature and humidity during pregnancy on TLBW.The interaction of temperature and humidity on TLBW was performed by likelihood ratio test,and the interaction index was calculated.In addition,the interaction between demographic characteristics and independent variables was analyzed.The distributed lag nonlinear model(DLNM)was used to divide the gestational period according to weeks and evaluate the correlation between temperature and humidity in different gestational weeks and TLBW,to identify the critical window period of exposure.DLNM does not allow missing values in the exposure matrix.Some subjects lacked exposure observation after birth.The model of the 37-week exposure matrix was called the "complete exposure model" and the model of the 42-week exposure matrix was called the "partial exposure model",the missing data were filled with the median of late pregnancy exposure as part of the sensitivity analysis.Results1.The incidence rate of TLBW:The total incidence rate of LBW and TLBW in the birth cohort was 3.16%(210/6640)and 1.36%(90/6640),respectively.In the study,the proportion of TLBW in offspring was 1.26%(78/6202),which was not significantly different from the incidence rate of TLBW in the birth cohort(χ2=0.17,P-0.68).2.Exposure level of ambient temperature and humidity during pregnancy:The median ambient temperature exposure(IQR)during pregnancy was 15.76(6.09)℃,and the median ambient humidity exposure(IQR)during pregnancy was 53.36(4.57)%.The Pearson correlation coefficient was 0.60(P<0.05).3.Effects of ambient temperature and humidity exposure during pregnancy on the risk of TLBW in offspring:Gam results showed that there was a significant nonlinear relationship between temperature and humidity exposure during pregnancy and TLBW risk(P temperature=0.02;P humidity=0.002).According to the results of GAM,pregnancy temperature and humidity were divided into three exposure levels.Compared with the medium level,low levels of temperature and humidity were associated with the risk of TLBW.The adjusted OR(95%CI)were 4.44(95%CI:1.65-11.42)and 6.23(95%CI:1.92-21.39),respectively.No statistical association was found between high levels of temperature and humidity and outcomes,The adjusted OR(95%CI)was 1.70(95%CI:0.59-4.83)and 1.85(95%CI:0.634.78),respectively.4.Interaction of ambient temperature and humidity exposure during pregnancy on TLBW:In the analysis of temperature humidity interaction,the likelihood ratio test shows that χ2=0.29,P=0.86,the test was not statistically significant.Interaction index S was 0.54(95%CI:0.11-2.55),interaction attributable proportion AP was-0.69(95%CI:-2.95-1.56),relative excess risk due to interaction RERI was-4.08(95%CI:-15.54-7.37).The three indicators showed that there was no statistical interaction between different levels of temperature and humidity on the outcome.5.Synergistic effects of population characteristics on the effects of ambient temperature or humidity exposure during pregnancy on TLBW:In the results of the humidity logistic model,the variables of hypertensive disorders of pregnancy in demographic characteristics were associated with TLBW,and the OR(95%CI)was 4.41(95%CI:1.98-8.73).In the results of the temperature logistic model,the variables of gestational hypertension were associated with TLBW,and the OR(95%CI)was 4.65(95%CI:2.09-9.23).The likelihood ratio test was conducted to determine whether there was an interaction between hypertension disorders of pregnancy and temperature or humidity at different exposure levels.The results showed no statistically significant interaction(Hypertensive disorders of pregnancy and temperature:χ2=1.98,P=0.37;Hypertensive disorders of pregnancy and humidity:χ2=5.64,P=0.06).6.The critical window period of the effect of ambient temperature and humidity exposure on TLBW during pregnancy:In the identification of the critical window period,for low-temperature exposure,it was not found that there was a statistical association with TLBW in each gestational week.Low humidity exposure was associated with the risk of TLBW from the first to the sixth gestational weeks.The OR(95%CI)from the first to the sixth gestational weeks were 1.92(95%CI:1.22-3.02),1.80(95%CI:1.18-2.75),1.69(95%CI:1.14-2.52),1.59(95%CI:1.10-2.31),1.50(95%CI:1.05-2.14)and 1.41(95%CI:1.00-1.99),respectively.7.Gender differences in the critical window period of the effects of ambient temperature and humidity exposure on TLBW during pregnancy:After stratification by sex of offspring,the maximum OR(95%CI)was 3.95(95%CI:1.70-9.16)for boys and 1.96(95%CI:1.06-3.63)for girls.In addition,meaningless high levels of temperature and humidity exposure in the effect analysis were still not associated with outcomes in the DLNM model.Conclusions1.The relationship between ambient temperature and humidity during pregnancy and TLBW was nonlinear.Lower levels of temperature and humidity exposure may increase the risk of TLBW.2.There may be no statistical interaction between temperature and humidity on TLBW.3.The critical window period of the effect of low humidity exposure on TLBW was in the early stage of pregnancy,and the adverse effect was greater in boys.4.The effect of low-temperature exposure on low birth weight may be cumulative.It is suggested that women pay attention to meteorological changes and avoid exposure to low ambient temperature and humidity during pregnancy,especially low humidity in the early stage of pregnancy,to reduce the risk of low birth weight.