Women living within half a mile from hydraulic fracturing sites are 25% more likely to have babies with low birth weight than mothers who lived more than two miles beyond the sites, according to a new study released Wednesday.

Why it matters: The findings by researchers at the University of Chicago, Princeton University and the University of California, Los Angeles suggests that hydraulic fracturing — a technique used to force out oil and natural gas from the earth — imposes negative health impacts on locals despite the enormous economic benefits it generates. While most drilling operations are in remote areas, some sites in places that are heavily populated.

However, the researchers told The Washington Post that their intention was not to condemn fracking, adding that “There’s a big effect within one kilometer of sites, which the oil and gas industry dislikes, but the impact on the population beyond that may not be massive, which opponents of fracking won’t like.”

How it was done: Researchers examined the weights of more than 1.1 million infants born to mothers living at different distances from active sites in Pennsylvania between 2004 and 2013, when hydraulic fracking transformed the state into a major producer of natural gas.