Association Between Short-term Exposure To Ambient Air Pollution And Meteorological Factors And The Risk Of Fetal Distress:A Matched Case-control Study

Background:Fetal distress is a pathophysiological status of fetal hypoxia,which is an important gestational complication.If the fetal hypoxia status cannot be corrected in time,it will develop into metabolic acidosis and asphyxia,resulting in fetal multi-system complications and even intrauterine death.The incidence of fetal distress in China is 2.7-38.5%.However,there is very limited research on the association between atmospheric pollutants and meteorological factors and the risk of fetal distress.Assessing the association between air pollutants and meteorological factors and the risk of fetal distress can provide theoretical reference for the prevention of fetal distress and the formulation of public health policy.Objective:1.To explore the association between short-term exposure to ambient air pollution and the risk of fetal distress,and identify the potential susceptible population and seasonal difference.2.To assess the association between short-term exposure to meteorological factors（temperature,relative humidity（RH）,diurnal temperature range（DTR））and the risk of fetal distress,identify the potential susceptible population and seasonal difference,and evaluate the interaction of temperature,RH and air pollutants on fetal distress.To explore the effects of non-optimal temperature and humidity（extreme temperature and RH）on fetal distress.Methods:The matched case-control study was established to estimate the association between maternal short-term exposure to ambient air pollution and meteorological factors and the risk of fetal distress.1.The medical data of women with fetal distress from 2013 to 2016 were extracted from the hospital information system of a large general hospital in Xi’an,and each woman with fetal distress was randomly matched with four women without fetal distress of the same age,same gestational week,and registration in the same period.The air pollutants exposure level was allocated according to the residential address of each participant using the inverse distance-weighted（IDW）interpolation method.2.Using conditional logistic regression model to estimate the odds ratio（ORs）of fetal distress and 95%confidence interval（CI）when the unit concentration of air pollutants changes.The association between extreme air pollutant concentrations exposure and the risk of fetal distress was estimated by using distributed lag non-linear model（DLNM）.Stratified analysis was used to identify potential susceptible population and seasonal difference.3.Conditional logistic regression model was used to assess the association between meteorological factors（temperature,RH,DTR）and the risk of fetal distress.Stratified analysis was used to identify potential susceptible population and seasonal difference.Interaction analysis was used to assess the interaction of temperature,RH and air pollutants on fetal distress.Using DLNM to estimate the association between exposure to non-optimal temperature and RH（extreme temperature and extreme RH）and the risk of fetal distress.Results:1.This matched case-control study included 313 pregnant women with fetal distress and1252 controls without fetal distress from 2013 to 2016.The average age of the participants was 28.5 years old and the average gestational age was 38.6 weeks.In the case group,72.2%of the participants were primipara,14.4%of the participants had gestational complications,4.2%of the participants had scar uterus,and 47.9%of the participants were admitted in the warm season.Similarly,in the control group,the above proportions were 67.8%,23.3%,6.6%and 45.6%,respectively.2.The levels of air pollutants and meteorological factors show obvious seasonal trends.PM₁₀,PM_2.5-10（PMcoarse,PM_C）,PM_2.5,SO₂,NO₂ and CO are high in winter and low in summer,while O₃ is high in summer and low in winter.The temperature and RH are high in summer and low in winter.During the study period,the daily mean levels of PM₁₀,PM_C,PM_2.5,SO₂,NO₂,CO,O₃,average temperature and average RH were 155.77μg/m³,75.28μg/m³,80.48μg/m³,33.88μg/m³,49.19μg/m³,1.90 mg/m³,78.34μg/m³,14.9℃and 60%,respectively.3.Maternal short-term exposure to PM₁₀,PM_C,SO₂,NO₂ and CO were significantly positively associated with the risk of fetal distress,and the cumulative effect was more apparent than the single-day effect.Among the single-day effects,the strongest effects of PM₁₀,SO₂,NO₂ and CO occurred in lag6.For every 10μg/m³ increase in PM₁₀,SO₂ and NO₂,the OR of fetal distress were 1.015（95%CI:1.003,1.027）,1.110（95%CI:1.041,1.185）and 1.148（95%CI:1.070,1.232）,respectively.For every 0.1 mg/m³ increase in CO,the OR of fetal distress was 1.025（95%CI:1.007,1.044）.Among the cumulative effects,the strongest effects of PM₁₀,PM_C,SO₂ and CO occurred in lag014,and the strongest effects of NO₂ occurred in lag010.For every 10μg/m³ increase in PM₁₀,PM_C,SO₂ and NO₂,the OR of fetal distress were 1.027（95%CI:1.004,1.050）,1.058（95%CI:1.014,1.105）,1.140（95%CI:1.029,1.264）and 1.158（95%CI:1.046,1.283）,respectively.For every 0.1 mg/m³ increase in CO,the OR of fetal distress was 1.029（95%CI:1.002,1.058）.In addition,compared with the median concentration,exposure to the 90th percentile concentration of PM₁₀,PM_C,PM_2.5,SO₂,and NO₂ were significantly associated with the risk of fetal distress.Stratified analysis showed that the association between air pollution and the risk of fetal distress was stronger among women over 30 years of old,women with gestational complications,and women admitted in the cold season,but the difference between different seasonal group was not statistically significant.In the two-pollutants model,after adjusting the pollutants with strong correlation（correlation coefficient greater than 0.7）,the association between air pollutants and fetal distress was no longer significant.4.There was no significant association between ambient temperature and the risk of fetal distress.RH was significantly positively associated with the risk of fetal distress.Among the single-day effects,the strongest effect occurred in lag10.For each 1%increase in RH,the OR of fetal distress was 1.014（95%CI:1.006,1.021）.Compared with the first quartile,exposure to the fourth quartile RH level,the OR of fetal distress was 1.834（95%CI:1.292,2.603）.Among the cumulative effects,the strongest effect occurred in lag014.For each 1%increase in RH,the OR of fetal distress was 1.020（95%CI:1.009,1.032）.Compared with the first quartile,exposure to the fourth quartile RH level,the OR of fetal distress was 1.803（95%CI:1.229,2.645）.Stratified analyses showed that the association between RH and the risk of fetal distress was stronger among multipara,women over 30 years of old,and women admitted in the cold season.The interaction of temperature and RH on fetal distress was not statistically significant,relative excess risk owing to interaction（RERI）:-0.316（95%CI:-1.085,0.453）,proportion attributable（AP）:-0.193（95%CI:-0.670,0.284）,synergy index（S）:0.668（95%CI:0.273,1.634）,product term:0.766（95%CI:0.450,1.305）.The additive and multiplicative interactions between RH and CO were significant,RERI:1.346(95%CI:0.129,2.563,AP:0.477(95%CI:0.205,0.748,S:3.822（95%CI:0.887,16.467）,product term:1.851（95%CI:1.022,3.352）.The interaction of temperature,RH and other air pollutants on fetal distress was not significant.5.The association between the extreme temperature defined by the three temperature variates（daily mean temperature,daily maximum temperature and daily minimum temperature）and the risk of fetal distress is not significant.Extremely high RH（95th,97th,99th percentiles）was positively associated with the risk of fetal distress,while extremely low RH（1th,3th,5th percentiles）was not significantly associated with the risk of fetal distress.The DTR at lag0 and lag01 was positively associated with the risk of fetal distress.The ORs were 1.051（95%CI:1.008,1.096）and 1.065（95%CI:1.012,1.121）,respectively.Conclusion:1.Maternal short-term exposure to air pollutants PM₁₀,PM_C,SO₂,NO₂,and CO was significantly associated with an increased risk of fetal distress,and cumulative effects more apparent than single-day effects.Exposure to extreme air pollutant concentrations was significantly positively associated with the risk of fetal distress.The association between air pollution and the risk of fetal distress was stronger among women over 30 years old,multipara,women with gestational complications,and women admitted in the cold season,but the difference between different seasonal group was not statistically significant.2.RH was significantly associated with an increased risk of fetal distress.The association between RH and the risk of fetal distress was stronger among multipara,women over 30 years old,and women admitted in the cold season.The association between ambient temperature and the risk of fetal distress was not significant.The interaction between temperature and RH on fetal distress was not significant,while there was a significant interaction between RH and CO on fetal distress.The association between extreme temperature and fetal distress risk was not significant.Extreme high RH was significantly positively associated with the risk of fetal distress.