The science on the health effects of fracking is still very much emerging. Oftentimes, the growing body of research can’t make a conclusive link between the drilling technique and negative health impacts, but it certainly makes the case that more research is needed. Earlier this month, another study joined the pack.

Published June 3 in the journal PLOS ONE, the study found that women who lived closer to a high density of fracking activity were more likely to have babies with lower birth weights than women living farther away from such drilling activity. The study is the first of its kind to be conducted in the Southwest Pennsylvania region, where drilling in the Marcellus Shale has grown from 44 wells before 2007 to nearly 2,900 wells drilled between 2007 and 2010. To conduct the study, researchers took data on birth outcomes among more than 15,000 babies born between 2007 and 2010 in the counties of Washington, Westmoreland and Butler and cross-referenced the information with the proximity of the mother’s home to unconventional gas drilling, which can include horizontal drilling and high-volume hydraulic fracturing (fracking). The mothers were divided into four groups according to the number and vicinity of wells within a 10-mile radius of their homes.

The researchers, all of whom hail from the University of Pittsburgh, found that women who fell in the top group for proximity were 34 percent more likely to have babies defined as being “small for gestational age” when compared to women who lived furthest from a high density of wells. The findings held even after researchers accounted for other variables that can contribute to low birth weight newborns, such as race, education, age, prenatal care and whether the mother smoked. The study did not find an association between proximity and density of drilling and premature birth.

According to the Centers for Disease Control and Prevention, low birth weight babies may be at heightened risk for health problems and infections. A birth weight of less than 5.5 pounds is considered low birth weight.

“Findings like ours can’t really be used to influence policy or even well intentioned things like patient-doctor interactions,” study co-author Bruce Pitt told me. “But hopefully it will lead to more precise research and that will form the evidence base we need to have important conversations between public health and policymakers on how to move forward.”

Pitt, chair of the University of Pittsburgh’s Department of Environmental and Occupational Health, told me his study follows similar research conducted in Colorado and which found an association between proximity and density of natural gas wells and congenital heart defects in infants. However, Pitt noted that due to geological differences, the potential effects of fracking will likely differ from community to community, and so research findings from one community aren’t necessarily applicable across the board. That’s why such fracking-related health research needs to be conducted region by region, he told me. For example, the study noted that previous research has found wide variations in methane emissions and benzene exposures among different drilling sites.

Pitt and his study co- authors Shaina Stacy, LuAnn Brink, Jacob Larkin, Yoel Sadovsky, Bernard Goldstein and Evelyn Talbott write:

In conclusion, a small but significant association between proximity to (unconventional gas drilling) and decreased birth weight was noted after accounting for a large number of contributing factors available from birth certificate data in Southwest Pennsylvania. Although the medical and public health significance of this is unclear, it was noteworthy that there was a significant increase in incidence of (small for gestational age) in the most exposed group. Along with the first published study on the association of increased incidence of birth defects and proximity and density of nearby wells in Colorado, there is a clear need for more complete studies including larger populations, better estimates of exposure and covariates and more refined medical records.

Pitt said while the findings aren’t definitive and don’t pinpoint the route of exposure — e.g., air or water — the gas drilling process does involve chemicals and contaminants known to be deleterious to infant health, such as benzene, fine particulate air pollution and heavy metals. In fact, he said infant health outcomes are a particularly good way to study the effects of fracking, as developing fetuses are especially sensitive to environmental pollutants.

Pitt said it’s time to make fracking-related health research a high priority, so “that we may safely transfer our resources and well-being to the next generation.”

“We feel it’s inarguable that more research is needed,” he told me. “I don’t think it’s reasonable to feel secure that we know enough about this…we need to look at these issues carefully and make our decisions rationally in terms of how to regulate in the future.”

To read a full copy of the Pennsylvania fracking study, visit PLOS ONE.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.