We’ve long known that poor air quality has a direct correlation on lung health and contributes to asthma, heart attacks and strokes, but new research has found a correlation between air pollution and the risk of miscarriage.

A study was conducted in Beijing, China, which is notorious for its pollution-choked skies. The study looked at health records of more than 255,000 pregnant women from 2009 to 2017, with researchers tracking pollution counts in their homes and at work by gathering data from air monitoring stations around the city.

Researchers found that 6.8 percent of the women had what’s called “silent miscarriages,” or miscarriages in the first trimester that showed no outward signs or symptoms. Factoring in ages, predispositions and other factors, researchers found that these instances occurred more frequently than in areas with lower pollution levels and concluded that exposure to pollution was associated with the risk of miscarriage.