Department of Research & Evaluation News

Exposure to a specific kind of air pollution, fine particulate matter, during pregnancy may significantly increase the risk of spontaneous preterm birth, which can be dangerous for both the mother and the baby, according to a Kaiser Permanente study published in JAMA Network Open.

“Consistent with other study findings, this current study has demonstrated that there is evidence of an independent association between exposure to ambient air pollution and preterm birth,” said Darios Getahun, MD, PhD, perinatal and pediatric epidemiologist with the Kaiser Permanente Southern California Department of Research & Evaluation. “However, these findings clearly demonstrated the association is between the exposure and spontaneous preterm birth rather than clinician-initiated labor.”

The study, which was conducted in conjunction with researchers at University of California, Irvine, and other institutions, found that pregnant women with lower socioeconomic status, less exposure to green space, more wildfire smoke, or extreme heat, were more vulnerable to the risk of spontaneous preterm birth from air pollution. The second trimester was identified as the most susceptible window.

The study looked specifically at an air pollution called PM2.5, which is fine particulate matter that is 2.5 micrometers or less in diameter, and related elements, such as black carbon and nitrates. It is often emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks, or fires, according to the U.S. Environmental Protection Agency. Most particles form in the atmosphere because of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries, and automobiles.

To examine the issue of preterm birth and air pollution, the researchers analyzed the electronic health records of more than 400,000 children delivered between 2008 and 2018 within the Kaiser Permanente Southern California. Researchers examined the associations between spontaneous preterm birth and exposure to PM2.5 as well as the additional effects of green space, wildfire-related exposure, and extreme heat during pregnancy.

“Our research adds to extensive evidence that communities facing socioeconomic challenges, limited green space, and heightened environmental stressors, such as wildfire smoke and extreme heat, are particularly vulnerable to maternal health impacts,” said corresponding author, Jun Wu, PhD, professor of environmental and occupational health at the UC Irvine Joe C. Wen School of Population & Public Health.

The study found that about 19,300 cases of spontaneous preterm birth (4.73% of total births) occurred among the patients in the study. Exposure to PM2.5 and its constituents, particularly black carbon, nitrate, and sulfate, was significantly associated with an increased risk of spontaneous preterm birth, especially in the second trimester. As the exposure to PM2.5 increased, so did the risk of spontaneous preterm birth. Patients who also were affected by lower education, lower income, living in areas with limited green space, or exposed to more wildfire smoke or extreme heat were at even higher risk for spontaneous preterm birth due to PM2.5.

Dr. Getahun suggested that “Health care providers should be aware of the high risk of spontaneous preterm birth among pregnant women who are socially stressed, such as with lower household incomes and residing in hazardous physical environments in order to minimize the burden of spontaneous preterm birth.”

This work was supported by the National Institute of Environmental Health Sciences and the California Air Resources Board.

Additional authors include senior author Chantal Avila, MA, Vicki Chiu, MS,  Jeff Slezak, MS, and David A. Sacks, MD, from the Kaiser Permanente Southern California Department of Research & Evaluation; John Molitor, PhD, from Oregon State University; Tarik Benmarhnia, PhD, from the University of California, San Diego; Jiu-Chiuan Chen, MD, from the University of Southern California; Alexa Reilly, BS, from Kaiser Permanente Bernard J. Tyson School of Medicine; Mengyi Li, MPH, Yi Sun, PhD, and lead author Anqi Jiao, BS, from the UC Irvine Joe C. Wen School of Population & Public Health. Dr. Getahun is also affiliated with the Kaiser Permanente Bernard J. Tyson School of Medicine.