High levels of air pollution appear to increase the chance of a “missed”, or silent, miscarriage, whereby the fetus dies during the first trimester, but the body does not recognize the pregnancy loss and no symptoms like bleeding occur.
The findings, reported in the journal Nature Sustainability, come from a large study recently carried out in Beijing, the smog-filled capital of China that has notoriously poor air quality.
A team of scientists from five Chinese universities analyzed the records of 255,668 women who were pregnant between 2009 and 2017, including almost 17,500 who experienced missed miscarriages. They then compared these figures with levels of maternal exposure to four major air pollutants, fine particulate matter (PM2.5), sulfur dioxide, ozone, and carbon monoxide.
After accounting for other factors, such as age and occupation, they found that increased levels of all four air pollutants were associated with a higher risk of missed miscarriage.
Silent miscarriages occur in up to 15 percent of all pregnancies, but they are especially common in developing countries. They occur when the fetus doesn't form or dies, but the placenta and embryonic tissues are still in your uterus.
It’s not clear exactly how air pollution might increase the risk of a silent miscarriage, however, this study is just one of many to show that being exposed to dirty city air during pregnancy can increase the risk of complications.
Thanks to another recent study, it’s also understood that soot and particulate matter from car engines and fossil fuel plants can be found in the fetal side of the placenta, meaning it might interact with or disturb fetal development.
Things don’t get much better after you're born, either. Air pollution has been linked to a whole bunch of respiratory conditions and cardiovascular diseases, including heart attacks, strokes, arrhythmia, heart failure, emphysema, and lung cancer.
To top it all off, a German study from earlier this year found that air pollution is responsible for nearly 9 million premature deaths each year, almost double the number estimated by previous studies.
“To put this into perspective, this means that air pollution causes more extra deaths a year than tobacco smoking, which the World Health Organization estimates was responsible for an extra 7.2 million deaths in 2015,” Thomas Münzel, co-author of the recent Germany study and a professor at the University Medical Centre Mainz, said in a statement.
“Smoking is avoidable but air pollution is not.”