Air pollution may increase the risk of miscarriage in early pregnancy

Poor air quality is one of the main factors leading to diseases. A large number of studies have shown that exposure of mothers to polluted air increases the risk of childbirth and may affect the health of mothers during pregnancy and even throughout their lives. However, little is known about the relationship between early pregnancy abortion and air pollution.

Professor Zhang Liqiang of Beijing Normal University and his collaborators analyzed the clinical records of more than 250,000 pregnant women in Beijing in the past 10 years and found that air pollution exposure was related to the increased risk of missed abortion during pregnancy. The relevant results were published in the journal Nature-Sustainability on October 14.

“The significance of this study is to remind pregnant women to take some protective measures consciously. On the other hand, I hope people will take more active measures to improve air quality and better protect their health. ” Zhang Liqiang said.

Human activities are the main reason for the increase of atmospheric concentration of trichlorofluoromethane. Source: Pixabay

Pollution exposure increases risk

Missed abortion means that the fetus has not yet formed or died, but the placenta and embryonic tissue are still missing in the mother’s uterus. The incidence of missed abortions is still high in many developing countries, Zhang said. Some countries have reported rates of up to 15%. Since China’s two-child policy was lifted in 2016, the impact of the environment on elderly pregnant women has been more obvious.

To find out the influence of the air pollution in Beijing missed abortion pregnant women, the researchers analyzed from 2009 to 2017, the clinical records of 255668 pregnant women, the city contains its education degree, occupation, living and working place, and according to their living and working place near the air monitoring stations (34) in the measurement data, the calculation for each air pollutant exposure levels in pregnant women. The pollutants involved include PM2.5 particles, sulfur dioxide, ozone, and carbon monoxide.

The researchers grouped the women into age at conception, occupation and ambient air temperature. Of the pregnant women who participated, 17,497 (6.8%) experienced missed abortions. “We found that the risk of missed abortion was related to the age of the pregnant woman and high and low temperatures outside.” “Said hou kun, a doctoral student at Beijing normal university. The study found higher rates of miscarriages among women over the age of 39, women farmers and blue-collar workers. Maternal exposure to various air pollutants was associated with missed abortion risk in all groups.

The researchers also found that for all four pollutants, the increased risk of missed miscarriage was associated with increased levels of the pollutant, as well as the time the woman was exposed to the pollution. “Our study found a quantitative relationship between them.” Zhang liqiang said. The risk increase is not linear, but non-linear with the increase of pollutant concentration.

Toxic Substances Attack Fetus

Regarding the impact of four types of air pollutants on missed abortion, Lin Jintai, co-author of the paper, associate professor and doctoral supervisor of the Department of Atmospheric and Marine Sciences of Peking University’s School of Physics, said carbon monoxide was the most influential, followed by sulfur dioxide.

“Toxic substances may attack developing fetuses by inducing immune changes through the placenta.” The author pointed out in the article.

Carbon monoxide may interfere with the metabolism and transport function of the placenta. After crossing the placental barrier, the concentration of carbon monoxide in the fetus may even be higher than that of the mother. In addition, environmental carbon monoxide is associated with carboxylated hemoglobin (COHb) and nucleated red blood cells. Excessive COHb in the mother’s body may make the fetus anoxic, leading to fetal death.

Zhang Liqiang said that the concentration of PM2.5 in the statistics ranged from more than 30 micrograms to more than 200 micrograms per cubic meter. However, due to the strong collinearity between PM2.5 and carbon monoxide, the author did not distinguish the respective effects of the two pollutants.

Studies have shown that prolonged exposure of pregnant women to air pollution may mean a higher risk of miscarriage, stillbirth and birth defects. The author also explores several possible causal mechanisms to explain this association. If the mother is exposed to PM2.5 for a long time, pollutants will cross the maternal-fetal blood barrier and affect the growth and development of the fetus. Pollutants entering the fetal blood may interact with its tissue components to produce pathological effects, causing irreversible damage to the fetal splinter cell and inducing anoxic damage or immune damage during the critical period of fetal development. In addition, related studies have also observed placental epigenetic changes caused by air pollution during the third month of pregnancy. This indicates that exposure of mothers to air pollution may damage placental function.

However, Zhang Liqiang stressed that the study only proved a correlation between air pollution and missed abortion, not a causal relationship. “Although we can adjust many known risk factors related to missed abortion, we cannot rule out residual confounding factors because we cannot control other factors such as traffic noise.” The author wrote in the article. In addition, the researchers said, due to the lack of relevant data, the impact of indoor air pollution on missed abortion is less studied, but indoor pollution is highly correlated with environmental pollution.

Further pollution reduction

“The health of a fetus affects the fate of a family or even a nation.” “Mr. Lin said. Reducing the risk of fetal death as part of the United Nations’ sustainable development goals, linking air pollution to the spatiotemporal variability of missed abortions, could enhance scientific and policy understanding of maternal health in developing countries.

This finding suggests that active pre-pregnancy measures may prevent or reduce harmful pregnancies. At the same time, the study helps understand the relationship between exposure to air pollution and a range of reproductive outcomes. “Pregnant women or people who want to become pregnant must protect themselves from the effects of air pollution, not only for their own health but also for the health of the fetus.” Zhang liqiang said.

He also said that as China has entered an aging society, the study provides additional impetus for the country to reduce environmental air pollution and increase the birth rate. Although environmental pollution in China has decreased in recent years, pollution levels remain high and must be further reduced.

“Studying the relationship between missed abortions and the environment is just the beginning.” “Mr. Lin said. Future work should explore the health benefits of reducing air pollution by using more data sources to model a wide range of environmental conditions.

References:

https://www.nature.com/articles/s41893-019-0387-y

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