Air Pollution in Pregnancy Linked to Higher Postpartum Depression Risk

Over the last 10 years, the U.S. has seen an alarming rise in postpartum depression, with incidence increasing from 9.4 percent in 2010 to 13.9 percent in 2021, according to the American Journal of Obstetrics and Gynecology. As doctors, advocacy organizations, and mothers work to lower these rates, there’s a growing need to identify the causes of postpartum depression, mitigate those risks, and ensure those at the highest risk are screened and have their concerns addressed.

As part of this effort, a new study from the Keck School of Medicine of University of Southern California sought to examine the effects of air pollution on postpartum depression. Published in the scientific journal Science of the Total Environment, the study analyzed data from 361 predominantly Hispanic/Latino mothers in Los Angeles, collected from pregnancy through early childhood, to measure the effects of environmental exposures on long-term health.

Using the Center for Epidemiologic Studies-Depression (CES-D) scale to measure depressive symptoms at 12, 24, and 36 months postpartum, the researchers cross-referenced this information with each participant’s exposure to outdoor air pollution based on their residential address. They calculated weekly average exposure levels during pregnancy for four pollutants: nitrogen dioxide (NO2), inhalable particulate matter (PM10), fine particulate matter (PM2.5), and ozone (O3). NO2 comes from the burning of fossil fuels in vehicles and power plants, while PM10 refers to particles less than 10 micrometers in diameter, including dust, pollen, and pollutants from factories and wildfires.

Results from the study revealed a nearly fourfold increase in postpartum depression risk in mothers who had higher exposure to air pollutants—specifically nitrogen dioxide or inhalable particulate matter during their second trimester— in comparison to those who had lower exposure. This increased risk persisted not only in the first year postpartum but extended up to three years after birth. Overall, 17.8 percent of women had depressive symptoms after one year, 17.5 percent after two years and 13.4 percent after three years.

“What’s really novel about this work is that we were able to extend the examination of depression beyond the first year postpartum, and have shown the sustained effect of air pollution during pregnancy on symptoms of depression all the way through three years postpartum,” Tracy Bastain, PhD, an associate professor of clinical population and public health sciences at the Keck School of Medicine of USC and senior author of the study said in press release. “Our study actually found a higher percentage of clinically significant depression compared to recent CDC data. That’s quite important—that there’s probably more postpartum depression out there than even our national prevalence data are showing.”

Given the results of their study, researchers see two clear actions that pregnant women and their doctors should take. For one, pregnant women should minimize their exposure to high levels of air pollution during the second trimester whenever possible. However avoidance simply isn’t possible for thousands of mothers who don’t have the time, means or ability to move. For these women, researchers recommend doctors keep a close eye on their mental health up to three years postpartum, identifying this increased exposure as a significant risk factor.

“Another important implication of our work is that depression can persist long beyond the first 12 months postpartum, and mothers should talk to their health care providers if they continue to have symptoms of depression,” Bastain said. “We’re continuing to drive this research forward so we can help protect the health of mothers and children for the long term.”