Increased area income improves birthweight rates, researchers find

UNIVERSITY PARK, Pa. — Higher incomes are often correlated with healthier pregnancies and babies, but is it really the money that matters? Sedimentary rocks that formed 390 million years ago, surprisingly, help provide the answer, at least for those who live above the Marcellus Shale formation, according to a team led by researchers at Penn State.

Using the Marcellus Shale economic boom — which originated with extracting natural gas from the formation and pumped billions of dollars into Pennsylvania between 2007 and 2012 — the researchers examined area incomes and birth weights, among other variables, in school districts sitting atop the black rock that stretches under much of Pennsylvania. In areas where the shale had the highest natural gas yield potential but not necessarily where wells were drilled, the researchers found an increase in area income across the socioeconomic spectrum led to a decrease in low birthweights, defined as less than five and a half pounds.

More specifically, in a group comprising 12,930 sibling pairs — one born pre-boom between 2005 and 2007 and another born post-boom between 2012 and 2013 — the researchers found the percentage of babies born at a low weight decreased by 1.5%, from 6.3% to 5.8%. The percentage change represents nearly 600 babies in the study born at higher birthweight, a key indicator for better health outcomes, according to the researchers. They published their findings in Demography.

“We know that infants who are born with low birthweight have greater risk of developing cognitive and health challenges, which are associated with lower educational attainment, lifetime earnings and adult health,” said lead author Molly Martin, professor of sociology and demography at Penn State. “What we didn’t know is whether income gains would improve pregnancy and infant health.”

Birthweight is tied to multiple health outcomes for babies, from immediate indicators, such as the ability to breathe, strength of their immune system and infant mortality, to long-term developmental factors and disease risk. To better understand how area income increases impact birthweight, pre-term birth rates, maternal health and behaviors before and during pregnancy, such as smoking and prenatal care compliance, the researchers used a “quasi-experimental” design. This is a common approach in the social sciences that can help estimate cause-and-effect relationships, not just identify correlations, among variables.

“It is impossible to randomly assign people to different lives with different resources,” Martin said, explaining that the shale formation provided an independent touchstone completely divided from any social or cultural influence. “All of the things that encourage or accompany an economic boom, such as development or job creation or pollution, influence outcomes at the surface. The areas of the shale formation with the greatest potential value serve as the predictor of economic improvement on the surface above.”

The Marcellus Shale economic boom served as a “natural experiment” of changing factors, Martin said. Her team used 21 datasets comprising information on demographics, taxes, births, expanded development like building roads for drilling well access, environmental impacts, including pollution, and more from national and state sources to crosscheck and control for potential confounding influences. The sibling group, which represented 271 districts, allowed the researchers to tighten controls even more and rule out things like differences in parenting style and genetic predisposition. With all factors made equal, income increase benefits came down to the potential economic value of the shale underpinning a community.

“Our map doesn’t focus on drilling but rather the potential economic impact based on the quality of the Marcellus Shale formation itself,” Martin said. “If communities lived above areas estimated to contain more natural gas, they had more money — even if drilling was not as extensive. And those communities had decreased rates of low birth weight.”

Income gains at the community level also led to a 1.8 percentage point increase in the rate of people receiving adequate prenatal care. However, income improvements did not bolster all pregnancy-related outcomes. Martin said they were surprised to find that they did not see improvements in pregnancy health and health behaviors — such as gestational weight or smoking rates.

Alexander Chapman, postdoctoral fellow in Penn State’s Edna Bennett Pierce Prevention Research Center, explained that their findings suggest income increases, even at the community-level, improve the well-being of pregnant people and their newborns, even if it doesn’t necessarily change individual behaviors.

“Income gains potentially reduce the number of stressors and hardships — or their consequences — leading to improvements in infant health,” Chapman said.

The researchers are continuing to examine the data to further explore how income gains affect children and families and inform public policies aimed at improving population health. According to Martin, their findings specifically highlight the benefits of community-wide economic improvements.

“This finding backs up other studies that show how important improvements in living standards are for health,” Martin said. “The development of the Marcellus Shale formation brought millions of dollars to parts of Pennsylvania, much more than the typical increases in targeted government funding for public assistance or infant health. The community-wide economic improvement benefitted people across the income spectrum.”

Tiffany L. Green, associate professor of obstetrics and gynecology and population health sciences, University of Wisconsin-Madison, also contributed to this project.

This work was supported by the Russell Sage Foundation, the National Institutes of Health, the National Institute on Drug Abuse, the Society of Family Planning Research Fund, the County Health Rankings and Roadmaps Program, Penn State’s Social Science Research Institute, Penn State’s Population Research Institute, Penn State’s Edna Bennett Pierce Prevention Research Center, and the University of Wisconsin’s Center for Demography and Ecology and School of Medicine and Public Health Centennial Scholars Program.