Beijing -- Chinese researchers have found a significant correlation between air pollution and the risk of miscarriage, according to a new scientific paper published on Monday.
While air pollution has been linked to increased risks of respiratory disease, stroke and heart attack, the new findings could add urgency to Beijing's efforts to control the problem. Air pollution has long plagued Chinese cities. Faced with a rapidly aging population, the government has been trying to raise the nation's fertility rate, which fell last year to its lowest level since 1949.
In a study published in the journal Nature Sustainability, scientists from five Chinese universities examined the rate of "overdue abortions" in the first trimester, which can be as high as 15 percent. Overdue abortion, also known as missing or delayed abortion, refers to the fetus has died but no signs of abortion, leading to parents mistakenly think that pregnancy progress is normal.
Zhang liqiang, a professor at Beijing normal university and lead author of the study, said such abortions are "particularly painful" for expectant parents, who often find out days or weeks later. He added that such abortions are not well studied, which is partly why researchers are concerned.
The study used clinical records of 255,668 pregnant women in Beijing from 2009 to 2017 to assess their exposure to air pollution from industry, homes, cars and trucks at home and at work. The researchers looked at four types of pollutants: deadly fine particulate matter known as PM2.5, sulfur dioxide, ozone and carbon monoxide. Pollution levels were calculated based on historical data collected by a network of air monitoring systems around Beijing. China's capital city is known for its grey smog.
Of the women in the study, 17,497, or 6.8 percent, experienced an overdue abortion in the first trimester. Taking into account differences in age, occupation and temperature, the researchers found that "maternal exposure to each air pollutant was associated with an increased risk of miscarriage in all populations."
Zhang liqiang, lead author of the study, said more research is needed to determine the exact link between different pollutants and the risk of overdue abortions. In the paper, funded by three Chinese government-backed research foundations, the authors acknowledge that data limitations make it difficult to account for other possible factors, such as indoor air pollution levels from stoves, building materials and tobacco smoke.
Even so, outside experts agree that the findings add to growing evidence that air pollution negatively impacts the health of pregnant women and their fetuses.
There is a lot of evidence that air pollution is associated with pregnancy outcomes in general, especially premature birth and the risk of low birth weight, said Tom Clemens, a lecturer at the university of Edinburgh who has studied the topic but was not involved in the study. "This is one of the first studies to link particulate pollution to pregnancy outcomes, and it's important in that sense."
Health concerns about air pollution have risen rapidly in China over the past decade. A recent study showed a link between air pollution and cognitive decline. Other studies suggest that air pollution in China causes as many as one million premature deaths each year.
This anxiety is mainly focused on children. Chai jing, a former journalist for China's state-run news media, has said that complications during pregnancy caused her to make a documentary about China's devastating air pollution. The documentary, titled "under the dome," went viral soon after it was released in 2015, and was suddenly ordered off the Internet by communist party censors.
Public concern about air pollution -- and its implicit threat to broader social stability -- has prompted government officials to try to address the problem. These efforts, including limiting the construction of coal-fired power plants and limiting the number of cars on the roads, have been largely successful. Beijing is on track to drop out of the world's 200 most polluted cities this year, according to a report released last month by AirVisual, the research arm of Swiss company IQAir.
But problems remain. Earlier this month, a thin layer of smog set the backdrop for a major celebration in Beijing marking the 70th anniversary of the founding of the People's Republic of China, despite the government's best efforts to control pollution. Footage of the parade showed Chinese military aircraft trailing colorful plumes of smoke through a polluted sky.
In the nature sustainable development paper, the researchers say the risk of an overdue abortion in the first trimester of pregnancy has decreased since 2013 as air pollution concentrations have declined -- further evidence of the link, they say.
At the end of the paper, they put the issue in the context of another official priority: China's declining birth rate. Worried about the possibility of a shrinking workforce, the government has encouraged women to have more children in recent years, partly by relaxing the one-child policy. But so far, these efforts have done little to change that trend.