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Lauren Petrie, of Food&Water Watch, holds up a photo of a fracking site near a playground and wears a mask to show opposition to COGCC board members during a public comment session on October 30, 2017 in Denver, Colorado. The Colorado Oil and Gas Conservation Commission (COGCC) will be deciding whether to approve the location of 84 wells Extraction Oil & Gas Inc wants to drill in Broomfield.

KEY POINTS Lauren Petrie, of Food&Water Watch, holds up a photo of a fracking site near a playground and wears a mask to show opposition to COGCC board members during a public comment session on October 30, 2017 in Denver, Colorado. The Colorado Oil and Gas Conservation Commission (COGCC) will be deciding whether to approve the location of 84 wells Extraction Oil & Gas Inc wants to drill in Broomfield. Helen H. Richardson | The Denver Post | Getty Images

Pregnant mothers who live near shale oil and gas fracking face an elevated risk of giving birth to babies with health problems, according to a landmark study. The finding comes as U.S. oil production is approaching all-time highs, driven by growth from U.S. shale fields. Producers in these areas use an advanced drilling method called hydraulic fracturing. These "frackers" inject water, sand and chemicals underground at high pressure to create a network of fractures in shale rock formations that allow oil and gas to flow. The method has long faced opposition from environmentalists concerned about potential groundwater contamination and air pollution caused by truck traffic and diesel emissions near fracking sites. The new study released Wednesday in the journal Science Advances raises fresh concerns about hydraulic fracturing's impact on infants.

These results suggest that hydraulic fracturing does have an impact on our health, though the good news is that this is only at a highly localized level. Janet M. Currie Princeton University professor of economics and public affairs

It is the first peer-reviewed research that shows large-scale evidence that fracking may negatively affect infant health. It was co-authored by economists from Princeton University, the University of Chicago and UCLA and based on a study of more than 1.1 million births between 2004 and 2013 in Pennsylvania, a major producer of natural gas from shale deposits. The study finds that babies born to mothers who live 1 kilometer, or about half a mile, from fracking sites are 25 percent more likely to be born at low birth weights. Infants born below 5.5 pounds are at greater risk of infant mortality, attention deficit hyperactivity disorder, known as ADHD, and asthma, according to the authors. The impacts on infants born 3 kilometers, or nearly 2 miles, from the sites were about one-half to one-third lower than those living 1 kilometer away. Beyond 3 kilometers, there were no observable impacts on infant health. "These results suggest that hydraulic fracturing does have an impact on our health, though the good news is that this is only at a highly localized level," Janet M. Currie, professor of economics and public affairs at Princeton University, said in a release. To be sure, few people live very close to these sites because most fracking occurs in remote rural areas in several parts of the United States. However, the authors note that oil and gas production is starting to encroach on more densely populated areas in some parts of the United States, including around Pittsburgh.

They estimate that 29,000 out of nearly 4 million U.S. births each year occur within 1 kilometer of a fracking site, while 95,000 babies are born to mothers who live within 3 kilometers. Study co-author Michael Greenstone, director of the Energy Policy Institute at the University of Chicago, said the findings may cause some communities to factor infant health into a discussion of the pros and cons of hydraulic fracturing. Previous research by Currie and Greenstone found that shale oil and gas activity boosts incomes, employment and housing prices in the areas where it occurs. They calculated an average benefit of $1,900 per household.