Maternal exposure to PM2.5 may increase the risk of congenital hypothyroidism in the offspring: a national data-based study in China
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Exposure assignment. The present study collected the monthly average levels of PM2.5, PM10 and AQI for 367 major cities in China from the 1st of January 2014 to the 30th of December 2015. These 367 cities were representative of the major prefecture-level cities of the 30 Chinese provinces (with the exception of Tibet, Taiwan, Hong Kong and Macau). In the present study, ambient air pollution exposure data were provided by the Chinese Air Quality Online Monitoring and Analysis Platform, which collected and released real-time and historical data on PM2.5, PM10 and AQI exposure levels (Chinese 2018). The data of this website originated mainly by the real-time data of ambient air monitoring that were recorded by the Ministry of Ecology and Environment of the People’s Republic of China. Each pollutant was continuously measured. PM2.5 was measured by β ray and Tapered Element Oscillating Microbalance, and PM10 was measured by light scattering methods. CH newborn screening. The annual incidence of CH in the 30 provinces in China from the 1st of October 2014 to the 30th of September 2015 was analyzed in the present study. The data were derived from the annals on the Chinese neonatal metabolic disease screening in 2015. It was compiled by the National Office of the Maternal and Child Health Surveillance (NOMCHS), based on the Chinese Newborn Screening information System (CNSIS), and published in the Chinese Maternal and Child Health Surveillance Network in February 2017(Yi Mou 2017). CNSIS is a screening program for newborns performed across the country, including the screening of CH. Whole-blood was collected from every newborn on filter papers for the measurement of the serum levels of thyrotropin (TSH) between 72 h and 7 days following birth. Premature, low birth weight or sick neonates and those who were discharged early within 7 days of birth were sampled within 20 days after birth. Any cases that indicated elevated TSH levels (higher than 10 to 20 μIU/ml) through double testing were followed-up and subjected to further diagnosis. Finally, the diagnosis of CH was confirmed by trained pediatric endocrinologists based on serum thyroid function tests (increased serum TSH, and reduced serum free thyroxine (FT4)). Each newborn diagnosed with CH was reported to local newborn screening centers (LNBSCs). Subsequently, a provincial newborn screening center (PNBSC) was established to guide and supervise the LNBSCs for all neonatal screening practices. The screening results reported by PNBSC were summarized and published by NOMCHS annually. The screening and diagnosis of the newborns adhered to the Technological Guideline on National Newborn Screening (2010) issued by the Ministry of health of the people’s republic of China. In addition, a written informed consent on CH screening was obtained from the neonates’ parents prior to the collection of their blood samples.
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A database-based study was conducted to analyze the association between air pollution exposure levels and the incidence of CH in 30 provinces in China. Annual exposure levels of PM2.5, PM10 and AQI were collected from the 1st of January 2014 to the 30th of December 2014. Considering that the exposed window of pregnancy is approximately 10 months, annual incidence of CH was collected from the 1st of October 2014 to the 30th of September 2015. The annual average exposure value of PM2.5, PM10 and AQI in each province was estimated in 2014 from monthly average exposure records of all cities included in each province by the weighted average method. Pearson correlation analysis was used to analyze the correlation among PM2.5, PM10 and AQI in 2014 and 2015. GeoDa version 1.10 was used to visualize the average incidence of CH in 30 provinces from the 1st of October 2014 to the 30th of September 2015. Furthermore, the incidence of CH in the 30 provinces was divided into high-incidence areas and low-incidence areas according to the 50th quantile (3.615 per 10,000 live births). Moreover, binary logistic regression analysis was used to estimate ORs and their 95% CIs between the risk of high incidence areas for CH and every 10 μg/m3 particle increase in the annual mean exposure levels to PM2.5, PM10 and in the mean AQI. Adjusted ORs were calculated by adjusting three pollution indicators mutually. On this basis, the effects of different exposure levels of air pollution on the risk of CH in the offspring were analyzed by calculating quartiles of mean PM2.5, PM10 and AQI exposure estimates, and identifying the cut-off value of air pollution exposure. The data were analyzed with the SPSS version 20.0. Significant results were considered at a P value lower than 0.05 (P < 0.05).