The first large-scale study to examine the health of babies born before and after natural gas extraction was introduced in Pennsylvania has found that pregnant women living in close proximity to fracking sites were more likely to give birth to underweight babies. The babies were also more likely to score lower on a standard index of infant health, the study showed.

A team of Princeton University health economists, led by Janet Currie, reviewed birth certificate data for 1.1 million children born in Pennsylvania between 2004 and 2013. The records included health information such as birth weight, as well as personal data on the mothers, including home addresses. The researchers compared the home addresses to locations of 7,700 fracking wells throughout the state. The majority of the fracking sites were developed after 2009, allowing the team to observe any changes in health before and after the introduction of fracking in specific areas.

“The development of hydraulic fracturing (“fracking”) is considered the biggest change to the global energy production system in the last half-century. However, several communities have banned fracking because of unresolved concerns about the impact of this process on human health,” wrote the study authors.

Currie and colleagues determined that children born within 1 kilometer (.62 miles) of a fracking site were 25 percent more likely to be underweight at birth, and had significantly lower scores on an infant health index. Children born within the range of 1 to 3 kilometers from a fracking site were still smaller in weight and showed signs of health effects, but the estimates were about one-third to one-half the size of those living closer.

Those living more than 3 kilometers away did not show any adverse health effects.

“There is little evidence for health effects at distances beyond 3 km, suggesting that health impacts of fracking are highly local,” the researchers conclude.

A low birth weight is considered anything less than 5.5 pounds and previous research has linked low birth weights to an increased risk of childhood mortality and poorer educational outcomes.

The team did factor in other potential influences on birth weight, such as the mother’s race, education and marital status. They also ruled out data on babies born in urban areas like Pittsburgh and Philadelphia because they already have high rates of low birth weights.

Unlike previous studies, the team also looked at scenarios with siblings – where one child was not exposed to any fracking sites, while the other was born near a fracking site – to help control for genetic factors.

Only 594 infants exposed to fracking had unexposed siblings, but the data was still helpful to draw an additional comparison, which showed that exposed infants were smaller than their unexposed siblings.

The study authors noted two specific reasons for focusing on infant health in relation to fracking. The first was that there is a growing body of evidence showing that the fetus is vulnerable to a range of maternal pollution exposures, but definitive conclusions in relation to fracking have not yet been determined.  Additionally, a fetus is in utero for at most nine months, making it easier for researchers to pinpoint the timing of any potential exposure. This presents a unique opportunity because in other cases such as cancer, the condition progresses over a long period of time.

The team believes that the exposure could be a result of either air pollution caused by fracking, or through wastewater with fracking fluids.

The study also addressed numerous limitations of similar work conducted previously. The sample size of the latest analysis is much larger than any other, and demonstrated how birth weights varied based on geographic distance from specific fracking sites. It also incorporated other health data in addition to birth weight.

The results suggest that a pregnant mother and her unborn child’s “exposure from proximity” could be the cause of low birth weight and adverse health effects, but further research is still needed. Future studies could include obtaining urine samples from pregnant women living near fracking sites to better determine the relationship between exposure and newborn health.

According to the study, informal estimates suggest that about 29,000 of the nearly 4 million annual U.S. births occur within 1 km of an active fracking site.

The study was published this week in Science Advances.

Fig. 1 Locations of births and fractured wells in Pennsylvania. Each square displayed above is 0.25° latitude by 0.25° longitude. We use all birth certificates in Pennsylvania for 2004–2013. Photo: Scientific Advances