Associations Between Prenatal Exposure To Polycyclic Aromatic Hydrocarbons And Thyroid Hormones In Umbilical Cord Blood

Objective:To explored the effect of prenatal exposure to polycyclic aromatic hydrocarbons on neonatal thyroid function,we evaluated the prenatal exposure level of polycyclic aromatic hydrocarbons and the thyroid function of newborns in Taiyuan,and we studied the relationship between maternal prenatal exposure to PAHs and neonatal cord blood thyroid hormone levels.Methods:We recruited the pregnant women-newborns as the research subjects delivered in the General Hospital of Taiyuan Iron and Steel(Group)Co.,Ltd.and the eighth people’s Hospital of Taiyuan City during the heating period in 2009-2010 and 2016-2017.They all signed informed consent forms before they were included in this study.We collected the basic data of pregnant women and newborns by face to face,and the questionnaire used was The questionnaire on the health status of pregnant women and newborns.The urine samples of pregnant women were collected by 30-50 m L and measured the specific gravity of urine and stored at-80 ℃,and the 50 m L of umbilical cord blood were collected and stored at-80℃.The concentrations of 11 PAHs metabolites in urine of pregnant women were determined by high performance liquid chromatography with tandem mass spectrometry(HPLC-MS/MS).The concentration of thyroid hormones in cord blood plasma were detected by the Luminex multi-factor flow fluorescence detection kit.The continuous variables of maternal age,pre-pregnancy BMI index,pregnancy BMI index,maternal head circumference,gestational age,and newborn head circumference,body weight and body length,which were in accordance with the approximate normal distribution and were expressed as mean ± standard deviation(SD).The classified variables of pregnant women’s education,mode of delivery,cooking and passive smoking during pregnancy,consumption of baked food,annual family income,traffic within 35 m from the house,parity,and sex of the newborn were expressed as numbers and frequency(%).The continuous variables in accordance with the skewed distribution of each PAHs metabolites and five thyroid hormones were expressed as the median and quartile range.Generalized linear model and restricted cubic spline(RCS)model were used to explore the relationship between PAHs metabolites and thyroid hormones.Results:In 250 pairs of pregnant women-newborns in two annuals of this study,we found that there were statistical differences in the basic information of pregnant women,such as maternal age,head circumference,consumption of baked foods during pregnancy,annual family income,parity and newborn body length,but no statistical differences were found in other basic information of pregnant women and newborns.Except for 1-OHPyr,there were significant differences in the distribution of PAHs metabolites between the two annuals.The median concentration of 2-OHPhe in urine of pregnant women was the highest(0.13 ng/m L)in 2009-2010.The median concentration of 2-OHNap in urine of pregnant women was the highest(0.37 ng/m L)in 2016-2017.Except for 3-OHFlu,the median concentrations of PAHs metabolites in 2009-2010 were lower than which in2016-2017.Except for FT3,the differences in the distribution of other hormones in neonatal cord blood plasma between the two annuals were statistically significant.The daily average concentration of 13 PAHs during the heating period in 2009-2010 in Taiyuan was apparently higher than 2016-2017.After adjusting the covariates including maternal age,maternal head circumference,pre-pregnancy BMI index,prenatal BMI index,maternal education,gestational age,parity,mode of production,annual family income,passive smoking of pregnant women,consumption of baked food,cooking during pregnancy,transportation within 35 m from the house,and newborn sex,weight,head circumference and body length,we found associations between maternal urinary PAHs and neonatal thyroid hormones in both years.In the whole,we found that there was a negative correlation between 2-OHPhe and T3,for each increased one unit of2-OHPhe after natural logarithmic conversion,T3 decreased by 0.07 units after logarithmic conversion,and the trend test showed that it was statistically significant(P=0.01);there was a negative correlation between ?-OHPAHs and T3,for each increased one unit of ?-OHPAHs after natural logarithmic conversion,T3 decreased by 0.10 units after logarithmic conversion,and the trend test showed that it was statistically significant(P= 0.001).According to the mode of delivery,the study population was divided into the natural delivery group and the cesarean section group.The results showed that in natural delivery group,urinary 2-OHPhe was negatively correlated with TSH(β=-0.10),and9-OHPhe,1-OHPhe and ?-OHPAHs in maternal urine were positively correlated with TSH(β= 0.17,β= 0.13,and β= 0.11),and urinary 1-OHPyr was positively correlated with cord blood T3(β= 0.07).2-OHNap,2-OHPhe,?-OHPAHs were all negatively correlated with T3(β=-0.06,β=-0.08,and β=-0.10).2-OHNap,9-OHPhe were separately negatively and positively correlated with FT3(β=-0.07 and β= 0.08).2-OHNap and 2-OHPhe were negatively correlated with T4(β=-0.03 and β=-0.04).1-OHPyr was positively correlated with T4(β= 0.07).In cesarean section group,1-OHNap was negatively correlated with TSH(β=-0.15),?-OHPAHs was negatively correlated with T3(β=-0.10),1-OHNap was negatively correlated with FT3(β=-0.12),1-OHNap and 1-OHPyr were separately negatively and positively correlated with T4(β=-0.10 and β= 0.09),1-OHNap was negatively correlated with FT4(β=-0.11).Then the study population was divided into boy group and girl group according to the sex of newborns.The results showed that in boy group,1-OHNap and 1-OHPhe were separately negatively and positively correlated with TSH(β=-0.15 and β= 0.15),1-OHPyr and 2-OHPhe were positively correlated with T3(β= 0.11 and β= 0.08),1-OHPyr was positively correlated with T4(β= 0.04).In the girl group,we found that9-OHPhe was positively correlated with TSH(β= 0.20),2-OHNap and ?-OHPAHs were negatively correlated with T3(β=-0.07 and β=-0.18),2-OHNap was negatively correlated with FT3(β=-0.05),1-OHPyr and ?-OHPAHs were separately positively and negatively correlated with T4(β= 0.12 and β=-0.06),and 1-OHPhe was positively correlated with FT4(β= 0.08).The results verified mode of delivery was a confounding factor to the study of effects of prenatal PAHs exposure on thyroid hormones in newborns,and There was a gender difference in the effect of prenatal exposure to PAHs on neonatal thyroid hormones.After stratifing the subjects in 2016-2017 according to the distance between the residence and the traffic trunk line(more than 35 m,within 35 m),we found that there were differences in the concentration of 2-OHFlu and 9-OHPhe between the two groups.Then associations between 9-OHPhe,TSH and FT4 were found in the group where the distance between the house and the traffic trunk line was less than35 m,but we not found associations in another group.The results showed that the traffic pollution may be one of the main sources of PAHs exposure of human in Taiyuan.Conclusions:This study explored the effect of prenatal exposure to PAHs on neonatal thyroid function mainly from an epidemiological perspective.The results found associations between prenatal exposure to PAHs and neonatal thyroid hormones,which has an inverse relationship between urinary 2-OHPhe in pregnant women and T3 in neonatal cord blood at birth,and which has a negative relationship between maternal urinary ?-OHPAHs and T3 in neonatal cord blood at birth.These results suggested that prenatal exposure to PAHs may be an important risk factor to affect the level of thyroid hormones in newborns;and they verified mode of delivery was a confounding factor to the study of effects of prenatal PAHs exposure on thyroid hormones in newborns,and There was a gender difference in the effect of prenatal exposure to PAHs on neonatal thyroid hormones,and the traffic pollution may be one of the main sources of PAHs exposure of human in Taiyuan.After optimizing the limitations in our study,we should further discuss the association between prenatal exposure to PAHs and thyroid function.Prenatal exposure to PAHs is closely related to neonatal thyroid hormones,prenatal exposure to PAHs affects neonatal thyroid function,therefore,focus and reduce the level of PAHs during pregnancy is significant for the healthy growth and development,we suggest that in order to create a healthier environment for prenatal women,the government should develop policies to regulate the level of PAHs and intake of food containing PAHs.