Another study has linked fracking, or hydraulic fracturing, to an increased risk of premature births. Above, a pump jack operates at a well site leased by Devon Energy Production Co. near Guthrie, Oklahoma, Sept. 15, 2015. Reuters/Nick Oxford

Expectant mothers have a lot to be concerned about, but those living near fracking sites have even more to fear, an expanding body of evidence shows. Most recently, a data review of more than 10,000 pregnancies has linked living in heavily fracked areas with a higher risk of premature births.

In the study, published Sept. 30 in the journal Epidemiology, scientists at Johns Hopkins University, Brown University and the University of California, Berkeley and San Francisco, analyzed data from the 10,496 pregnancies of 9,384 mothers in nearly 700 communities in Pennsylvania from 2009 to 2013. At the same time, they tracked shale gas drilling, fracturing and production in a 12.4-mile radius of each woman.

What they found was that mothers who had higher exposure to these operations and infrastructure -- in essence, those who had more drilling and fracking sites in the vicinity of their homes -- were 40 percent more likely to give birth to premature babies. They were also 30 percent more likely to have high-risk pregnancies, the researchers found.

"Any form of energy extraction that harms the well-being of infants and pregnant women has no place in society," Sandra Steingraber, a biologist with the organization Americans Against Fracking, who was not involved in the study, said in response to the new findings. "These data show that a ban on fracking is good prenatal care."

Fracking, or hydraulic fracturing, is the process of injecting millions of gallons of sand and chemical-laced water into gas-rich shale below the earth to allow gas to be released from the rock. Those liquids are then brought back to the surface of the earth. Previous studies have linked living near fracking sites to infertility, miscarriages and birth defects. Researchers have blamed the increased risk of exposure to toxic chemicals and even radioactive materials.

More than 15 million people in the U.S. were living within one mile of a fracking well, Al Jazeera reported in 2014, as the practice has increased significantly in the U.S. in recent years. Advocates say fracking helps communities by creating jobs, while critics argue it can be detrimental for human health and to the environment.