Recently, the team of Cai Jing/Kan Haidong of our hospital, together with the team of He Yuan/Ma Xu of the Institute of Science and Technology of the National Health and Wellness Commission, made progress in the study of PM2.5 exposure during pregnancy, the risk of premature delivery and the burden of disease. The research results are "Composition of Fine Particulate Matter and Risk of Preterm Birth: A Nationwide Birth Cohort Study in 336 Chinese Cities" and "Improved air quality" and reduced burden of preterm birth in China: 2013– 2017 "was published online in Journal of Hazardous Materials and Science Bulletin.
Reducing maternal and neonatal deaths is an important part of the United Nations sustainable development goals. Premature birth (PTB) is not only the main cause of neonatal morbidity and mortality, but also an important factor leading to the death of children under 5 years old. According to WHO estimates, about 15 million premature babies are born every year in the world, which has caused a heavy burden to society and families. Previous studies have shown that the occurrence of premature delivery is related to PM2.5 exposure during pregnancy; However, the results of existing studies are inconsistent, and the specific functions of various chemical components of PM2.5 are still unclear. In addition, in order to improve the severe air pollution situation, in September 2013, the Chinese government issued "Air Pollution Prevention Action Plan" with ten measures (hereinafter referred to as "Air Ten") to control air pollution nationwide. Since the implementation of this policy, the air quality level in various parts of China has improved significantly. However, the long-term impact of this policy on the burden of premature delivery in China and the difference in time and space distribution of this impact have not been studied. Evaluating the impact of this policy is of great significance for continuing to promote the formulation and improvement of relevant policies and regulations, and conducting timely risk communication to the public to reduce the risk of premature delivery of PM2.5.
In view of the above problems, the research group carried out a nationwide cohort study based on the national pre-pregnancy eugenics health examination project. Quantitative evaluation of PM2.5 and its main chemical components (OC, BC, SO42− , NH4+ and NO3− ) the risk of premature delivery. In this study, a satellite prediction model with high temporal and spatial accuracy was used to simulate the exposure of pregnant women to PM2.5 and its chemical components during pregnancy. Under the control of demographic characteristics, individual and lifestyle factors of pregnant women, seasonal and spatial variation, Cox regression was used to analyze the exposure-response relationship, and possible sensitive subgroups were identified by hierarchical analysis.
A total of 3.72 million newborns were included in the study, of which 7.7% were born prematurely. For every quartile interval (29 μ G/m3), the risk of premature delivery increased by 7% (HR: 1.07; 95% confidence interval CI: 1.07– 1.08) (Figure 1). All the components were significantly related to the occurrence of premature delivery, among which two carbon-containing components OC and BC caused the greatest risk of premature delivery, with HR of 1.09 (95%CI: 1.08– 1.10)。 Women who are older in pregnancy, exposed to second-hand smoke during pregnancy, overweight or obese before pregnancy, pregnant in winter, and living in northern or rural areas of China are more susceptible. Different types of premature delivery (very premature delivery, delivery at 20-31 gestational weeks; Moderate premature delivery, delivery at 32-34 gestational weeks; And late premature delivery, delivery at 35-36 gestational weeks), late premature delivery is more sensitive to PM2.5 and various components (except OC and SO42-), which may be due to other more serious risk factors in extremely premature delivery and moderate premature delivery, which may "cover up" the harmful effects of PM2.5 and its components.
Fig. 1. The risk ratio of premature delivery caused by the increase of IQR units in the concentration of total PM2.5 and its components in different pregnancy periods.
Based on the same database, the research team further analyzed the temporal and spatial changes of the disease burden of premature delivery caused by PM2.5 exposure during pregnancy. By comparing the difference of disease burden between 2013 and 2017, the impact of the "Ten Atmosphere" policy was evaluated, and the spatial distribution of the disease burden of premature delivery caused by air pollution was drawn in a grid (1 km resolution). The results show that after the implementation of the "Atmosphere Ten" policy, the population-weighted PM2.5 concentration in China has dropped significantly. Even though the number of newborns has increased in 2016, we still observe the reduction of the burden of PM2.5-related premature birth diseases. According to the global air quality guide (2021) issued by WHO, the average concentration limit of IT-4 in PM2.5 years is 10 μ With g/m3 as the reference concentration, the number of premature infants in China due to PM2.5 exposure during pregnancy reached 283,726 (95% CI: 273,257 & ndash; 294,040), and in 2017, this number dropped to 270,539 (95% CI: 260,192 & ndash; 280,766), the attribution score of premature delivery caused by PM2.5 exposure also changed from 28% (95% CI, 27%– 29%) to 23% (22%– 24%) (Figure 2). The reduction of the burden of premature delivery during pregnancy is more obvious in areas such as Beijing-Tianjin-Hebei and the middle and lower reaches of the Yellow River, where pollution was serious in the past. howeverAt present, the burden of PM2.5-related premature birth diseases in China is still higher than that in other developed countries, so it is still necessary to continuously improve air quality.
Based on the national birth data with the largest sample at present, these two studies quantitatively analyzed the risk of premature delivery caused by exposure to PM2.5 and its chemical components in China, calculated the burden of premature delivery caused by PM2.5 during pregnancy, and evaluated the impact of the implementation of the "Atmosphere Ten" policy on adverse birth outcomes. The above findings have important public health significance, and provide corresponding scientific basis for relevant departments to formulate policies and regulations to protect maternal and infant health. At the same time, these research results also have important reference value for other low-income and high-pollution countries in the world.
Figure 2. China’s 2013– Population-weighted PM2.5 concentration (a), premature delivery attribution number (b) and attribution score (c, d) in 2017.
Jiang Yixuan, a Ph.D. candidate from School of Public Health of Fudan University, and Associate Professor He Yuan from Institute of Science and Technology of National Health and Wellness Commission are co-first authors, Professor Ma Xu from Institute of Science and Technology of National Health and Wellness Commission and Associate Professor Cai Jing from School of Public Health of Fudan University are co-authors, and Professor Kan Haidong from School of Public Health of Fudan University is a senior author. The two studies were supported by national key R&D programs (2016YFC1000102, 2016YFC1000307, and 2016YFC0206202), major research program integration program of National Natural Science Foundation of China (91543114), and Shanghai Natural Science Foundation (20ZR1402900).