Fifteen years after the collapse of One World Trade Center in New York City, researchers are still learning how the terrorist attacks of September 11, 2001, impacted people’s health.

When the twin towers fell on 9/11, a cloud of hazardous materials enveloped the surrounding neighborhood and coated everything and everyone exposed to it for several days. According to a new study, those dust clouds likely contributed to negative birth outcomes for Lower Manhattan mothers. (See pictures reflecting on 9/11 from the 15th anniversary of the attacks.)