Exposure to common air pollutants during early pregnancy may increase the likelihood of persistent depressive symptoms throughout pregnancy, according to a new study led by Tracy Bastain and co-authored by Carrie Breton, who recently joined Bursky School of Public Health at Washington University in St. Louis.
The study on early exposure to air pollution was published June 2 in Environmental Health. It draws on data from the MADRES (Maternal And Developmental Risks from Environmental and Social Stressors) cohort, a long-running study of predominantly low-income Hispanic and Latina women in Los Angeles conducted through the MADRES Center of Excellence on Environmental Health Disparities.
Before joining WashU Bursky Public Health, Bastain and Breton helped build and co-lead the nationally recognized center, which has followed more than 1,000 families for the last 10 years to understand how environmental exposures, social stressors and community conditions shape maternal and child health, particularly among populations disproportionately affected by health disparities.
Although the cohort remains based in Los Angeles, the MADRES research program is now jointly housed at WashU and the University of Southern California.
For the study, researchers followed 542 women participating in the MADRES cohort. Participants completed depression screenings during each trimester of pregnancy, allowing researchers to track how symptoms evolved over time rather than measuring depression at a single point.
Depression during pregnancy affects an estimated 10% to 20% of women worldwide and has been linked to adverse health outcomes for mothers and children, including postpartum depression, preterm birth and developmental challenges in childhood.
While previous studies have linked air pollution to an increased risk of depression, most have assessed symptoms at a single point in time or relied on medical diagnoses. This study instead examined how depressive symptoms changed throughout pregnancy and whether daily exposure to air pollution before conception and during early pregnancy influenced those patterns.
Early pregnancy may be a critical window
Researchers found that higher air pollution in the first six weeks impacted the trajectory of depressive symptoms over pregnancy.
“Our findings suggest that the earliest weeks of pregnancy may represent a particularly sensitive period when environmental exposures can influence maternal mental health,” said Bastain, a professor of public health. “Understanding these risks may help identify opportunities to better support women during pregnancy.”
The findings are biologically plausible, researchers said. Early pregnancy is marked by dramatic hormonal and neuroendocrine changes that help support fetal development and prepare the body for pregnancy. Previous studies suggest that air pollution can trigger inflammation, oxidative stress and activation of the body’s stress-response system, all of which have been linked to depression and other mood disorders.
The researchers hypothesize that air pollution may interfere with these early physiological adaptations, potentially affecting pathways involved in stress response and mood regulation.
Researchers identified four distinct patterns of depressive symptoms during pregnancy: About 43% of participants maintained consistently low symptom levels throughout pregnancy; 35% followed a moderate-to-low symptom pattern; nearly 15% experienced consistently moderate symptoms; and 7.4% experienced persistently elevated symptoms, with symptoms peaking around mid-pregnancy.
Clinically relevant depressive symptoms were most common during the first trimester. Twenty-six percent of participants scored above the threshold for clinically relevant depression early in pregnancy, compared with 19% in the second trimester and 17% in the third.
Women exposed to higher levels of several common air pollutants during early pregnancy were more likely to experience clinically relevant depressive symptoms throughout pregnancy than women with lower exposures.
The strongest association was observed for nitrogen dioxide, a pollutant commonly associated with vehicle traffic. Participants with higher nitrogen dioxide exposure during the first six weeks of pregnancy were 3.82 times more likely to follow the highest-symptom trajectory than the lowest-symptom trajectory.
Unlike many environmental hazards, these pollutants are part of the air people breathe every day. Nitrogen dioxide is commonly produced by traffic emissions, while particulate matter consists of microscopic airborne particles generated by sources such as vehicles, industry and wildfires.
Because these exposures are widespread, even modest increases in risk could have important public health implications.
While the study focused on pregnancy, the researchers emphasized that there are practical steps anyone can take to reduce exposure to air pollution. These include exercising away from busy roads or during periods of lighter traffic, as well as using air conditioning or air filters indoors to improve air quality. Reducing exposure can have health benefits throughout life, not just during pregnancy. “Reductions in air pollution emissions are also a big part of the strategy to protect everyone,” Bastain said.
Environmental and social factors may work together
The study also highlighted the importance of social determinants of health. Women in the highest-symptom groups were more likely to be Black, have a history of depression or antidepressant use, and be less likely to be living with a partner during pregnancy. This is consistent with well-documented disparities in maternal mental health, the researchers said. Black mothers experience higher rates of prenatal and postpartum mental health conditions and are more likely to encounter social and structural challenges, including discrimination and barriers to accessing culturally responsive care.
“It is always a challenge to tease out all of the possible contributing factors that may account for higher trajectories of depression during pregnancy,” Bastain said. “However, the associations we observed between air pollution exposure and depressive symptom trajectories remained consistent after accounting for multiple potential confounding factors.”
The findings suggest that environmental exposures may interact with social and structural factors that influence maternal mental health. Researchers noted that social support, access to care and broader inequities likely play important roles alongside environmental influences.
“Maternal mental health is shaped by multiple factors,” said Breton, a professor of public health. “Understanding how environmental exposures intersect with social conditions can help identify populations that may be at greater risk and inform strategies to support healthier pregnancies.”
