Researchers analyzed data from more than 1 million births in Pennsylvania from 2004 to 2013. Babies born to mothers living up to 1.8 miles from a fracking site were found to have poorer health, and babies born within 0.6 miles saw the largest impacts, according to a study published in Science Advances. The findings could have implications for where fracking is authorized.

Previous studies have shown that fracking causes air pollution that can harm babies, and that living nearby fracking sites is linked to premature births. Today's study adds to the evidence that the shale gas boom comes with some serious side effects. "There's growing evidence that living close to unconventional natural gas development might have implications for population health," says Joan Casey, a postdoctoral researcher at the University of California, Berkeley, who was not involved in the research. "This is one of the largest studies to date showing that."

Fracking, short for hydraulic fracturing, uses a high-pressure mixture of water, sand, and chemicals to crack sediment layers so that oil and natural gas can be tapped. The technique has revolutionized the energy landscape in the US, lowering energy prices and reducing dependance on coal. But it's also alarmed scientists and activists alike for its potential to pollute groundwater, affect air quality, and cause earthquakes.

As several states like New York and Maryland have banned fracking, scientists are trying to figure out what impacts the controversial extraction technique has on health - especially when it comes to newborns. A 2014 study, for example, found that children born to mothers living nearby fracking sites may have a higher risk of heart defects. "Looking at the impacts of these chemicals on the most vulnerable population, which is unborn children, and finding these effects is really concerning," says Carol Kwiatkowski, the executive director of the nonprofit research institute The Endocrine Disruption Exchange.