A new study by NIEHS-funded researchers found that pregnant women who lived near active oil and gas wells were at higher risk of having low birth weight babies. The birth cohort study, published in the journal Environmental Health Perspectives, is one of the largest of its kind and the first in the state of California.

Oil and gas extraction spans decades in many states. Public health researchers are beginning to explore a variety of health outcomes from resultant environmental exposures of active and inactive sites.

Being small for gestational age or being born at low birth weight can affect development and risk of health problems in childhood and later life, according to the study authors. Small for gestational age is a term used to describe a baby who is smaller than the usual size for the number of weeks of pregnancy. Low birth weight refers to a newborn who weighs less than 5 pounds, 8 ounces.

Boyles manages grants for studying effects of pollutants on reproduction and birth outcomes, such as low birth weight and preterm birth. (Photo courtesy of Steve McCaw)

“Pregnant women living near oil and gas developments are exposed to a variety of hazards, not only chemicals in the air and water, but also noise, odors, and traffic,” said Abee Boyles, Ph.D., NIEHS program officer. “This study was able to narrow in on the impacts of living in close proximity to active wells, as opposed to more general areas near these activities.”

NIEHS grantee Rachel Morello-Frosch, Ph.D., along with doctoral candidate Kathy Tran from the University of California (UC) at Berkeley, led the study. Another author, Joan Casey, Ph.D., from Columbia University, was supported by an NIEHS Pathway to Independence Award. That grant program helps postdoctoral researchers launch careers.

Impacts during sensitive perinatal period

NIEHS research has suggested that during periods of rapid growth and development, normal biological processes are more readily disrupted by exposures.

To better understand the link between the environment and birth outcomes, the researchers analyzed nearly 3 million birth records in California. The babies were born from 2006 to 2015 to mothers living within 6.2 miles of at least one active or inactive well site.

An intimate look at the data

For the first time in a study like this, researchers compared outcomes for women living in rural and urban areas, and near active and inactive sites.

The team reported that in rural areas, pregnant women who lived within 0.62 miles of the highest producing wells were 40% more likely to have low birth weight babies than those living further away or near inactive sites. The same group of women were 20% more likely to have babies small for their gestational age. Their full-term babies were 1.3 ounces — or 30 grams — smaller on average than babies whose mothers lived farther from active sites.

Women living in urban areas close to high-production wells were 4% more likely to have a small for gestational age infant.

“When you see a shift of over 30 grams of birth weight among [full-]term infants, from an individual clinical perspective, it may not seem like a lot,” said Morello-Frosch, as quoted in a UC Berkeley press release by Kara Manke. Morello-Frosch stressed that such a shift can have significant implications at the population level for infant and children’s health.

“Results from health studies such as ours support recent efforts to increase buffers between active wells and where people live, go to school, and play,” said Morello-Frosch. (Photo courtesy of Rachel Morello-Frosch)

Reasons still unclear

To separate impacts of oil and gas sites from other factors that might play a role in birth outcomes, the team controlled for maternal education, race, ethnicity, area-level socioeconomic status, and levels of traffic-related air pollution, among other characteristics.

Reasons for the differences in birth weight between urban and rural locations were unclear, according to the authors. They suggested that maternal occupation, indoor air quality, or other aspects of housing conditions might be responsible.

“In addition to being one of the largest retrospective cohort studies to date, this study associated active production of oil and natural gas with adverse outcomes for the developing fetus,” said Boyles. “Further exploration of the urban and rural differences could inform preventative measures such as indoor air filters or personal protective equipment for certain occupations, to protect pregnant women and their children.”

Learn more about the study in a June 18 article the authors wrote for The Conversation.

Citation: Tran KV, Casey JA, Cushing LJ, Morello-Frosh R. 2020. Residential proximity to oil and gas development and birth outcomes in California: a retrospective cohort study of 2006–2015 births. Enviro Health Perspect 128(6):67001.

(Sheena Scruggs, Ph.D., is a digital outreach coordinator in the NIEHS Office of Communications and Public Liaison.)