(CNN) Pregnant women who have been exposed to high levels of pollution face an increased risk of "silent miscarriage" in the first trimester, according to a new study. A "silent miscarriage" happens when a fetus hasn't formed or has died, but the placenta and embryonic tissue remain.
Researchers analyzed data from more than 250,000 pregnant women in Beijing between 2009 and 2017. The study published Monday in the journal Nature Sustainability.
Earlier research has shown a connection between pollution and health problems for pregnant women, such as hypertension and pre-eclampsia. Pollution is also linked to low birth weight, but there has been little research to connect pollution to miscarriage.
This study found that the women who lived in neighborhoods in Beijing with higher levels of concentrated pollution including particulate matter pollution, sulfur dioxide, ozone and carbon monoxide saw a greater risk of miscarriage. Particulate matter pollution seemed to put the women at the greatest risk among miscarriages linked to pollution. The authors thought that was because these tiny particles can cross the maternal-fetal blood barrier and disrupt fetal growth and development.
This study seems to agree with earlier work. A study in that United States published in February found that women in Utah who were exposed even short-term to pollution faced an increase risk of miscarriage.
Other research has found that pollution can breach a mother's placenta and potentially reach fetuses in the womb, raising the possibility of miscarriage or, if the woman is able to carry the baby to term, future health problems for the child.
A 2017 study of women in London found that exposure to pollution from traffic led to giving birth to low birth weight babies. Babies born with a low birth weight are at a much greater risk of dying than healthy weight babies and face a much greater risk of chronic disease later in life, such as cardiovascular problems.
When these tiny pollution particles enter the fetal bloodstream, they may interact with the tissue leading to irreversible damage to the dividing cells. Maternal exposure may also damage the placenta.
Women who were older than 39 at age of conception and women who worked as farmers or as blue collar workers seemed to be most at risk.
Earlier studies have shown that even when air pollution is at levels below air quality guidelines and regulatory limits, it can still pose a real hazard to public health. Exposure to high levels of pollution have lead to an increasing number of deaths around the world.
A study in July found that long-term exposure to air pollution, especially ground-level ozone, is like smoking about a pack of cigarettes a day for many years and can cause problems such as emphysema. Another study found that it can cause COPD and age lungs faster. Air pollution also increases the risk of heart disease, stroke and lung cancer.