Hydraulic fracturing, or "fracking," is already a controversial issue, and new research suggests pregnant women who live near natural gas wells where this process takes place are more likely to have babies with low birth weights.

While the findings did not determine the proximity to the wells at which this effect may occur, it does call for further investigation into the concerning link, University of Pittsburgh Schools of the Health Sciences reported.

"Our work is a first for our region and supports previous research linking unconventional gas development and adverse health outcomes," said co-author Bruce Pitt, chair of Pitt Public Health's Department of Environmental and Occupational Health. "These findings cannot be ignored. There is a clear need for studies in larger populations with better estimates of exposure and more in-depth medical records."

To make these findings, a team of researchers 15,451 babies born in Washington, Westmoreland and Butler counties between 2007 and 2010. The participants were broken into groups based on the number and proximity of fracking wells within 10 miles of their homes.

The researchers found women whose homes had the highest density of wells were 34 percent more likely to have babies who were "small for gestational age" than women in the group with the lowest concentration of wells. Small for gestational weight refers to babies who are below the smallest 10 percentile.

"Developing fetuses are particularly sensitive to the effects of environmental pollutants," Pitt said. "We know that fine particulate air pollution, exposure to heavy metals and benzene, and maternal stress all are associated with lower birth weight."

The researchers stressed the study does not conclusively determine fracking-related pollutants cause lower birth weights, and further investigation is required.

The findings were published in a recent edition of the journal PLoS ONE.