Early pregnancy pollution tied to lasting depressive symptoms in study

Exposure to common air pollutants in the opening weeks of pregnancy was associated with more persistent depressive symptoms, according to a study led by researchers Tracy Bastain and Carrie Breton. The findings add air quality to the list of factors researchers say may affect maternal mental health during a period already tied to risks for mothers and children.

The study, published in Environmental Health, used data from the MADRES cohort, a long-running Los Angeles study focused on maternal and child health among predominantly low-income Hispanic and Latina women. Washington University in St. Louis said the MADRES program has followed more than 1,000 families over the past decade and is now jointly housed at WashU and the University of Southern California.

For this analysis, researchers followed 542 pregnant participants. The women completed depression screenings in each trimester, allowing the team to study symptom patterns across pregnancy rather than relying on one screening or a diagnosis in medical records.

Washington University said depression during pregnancy affects an estimated 10% to 20% of women worldwide. The condition has been linked in prior research to postpartum depression, preterm birth and developmental challenges in childhood.

First six weeks stood out

The researchers reported that higher air pollution exposure during the first six weeks of pregnancy was linked to different symptom trajectories over the rest of pregnancy. Bastain, a professor of public health, said the earliest weeks may be a sensitive period when environmental exposures can affect maternal mental health.

The team identified four patterns of depressive symptoms. About 43% of participants had low symptoms throughout pregnancy, 35% moved from moderate to low symptoms, nearly 15% had consistently moderate symptoms and 7.4% had persistently high symptoms that peaked around mid-pregnancy, according to the study.

Clinically relevant depressive symptoms appeared most often in the first trimester. Researchers reported that 26% of participants crossed that screening threshold early in pregnancy, compared with 19% in the second trimester and 17% in the third.

The strongest association involved nitrogen dioxide, a pollutant commonly tied to traffic emissions. Participants with higher nitrogen dioxide exposure in the first six weeks were 3.82 times more likely to fall into the highest-symptom group than the lowest-symptom group, according to the study.

The researchers also examined particulate matter, which Washington University described as microscopic airborne particles produced by sources including vehicles, industry and wildfires. The study did not present the findings as proof that pollution causes depression, but researchers said the associations remained after accounting for multiple potential confounding factors.

Biology and social factors

The research team said the association is biologically plausible because early pregnancy involves major hormonal and neuroendocrine changes. Prior studies cited by the researchers have linked air pollution to inflammation, oxidative stress and activation of the body’s stress-response system, pathways also connected to mood disorders.

The study also found that women in the highest-symptom groups were more likely to be Black, to have a history of depression or antidepressant use, and to be less likely to live with a partner during pregnancy. The researchers said those findings fit with documented disparities in maternal mental health and with barriers tied to discrimination, social conditions and access to culturally responsive care.

Breton, a professor of public health, said maternal mental health is shaped by many factors and that studying environmental exposures alongside social conditions may help identify groups at greater risk. Researchers said social support, access to care and broader inequities likely operate alongside pollution exposure.

Washington University said people can reduce exposure by exercising away from busy roads or during lighter traffic periods and by using air conditioning or indoor air filters. Bastain also said lowering air pollution emissions is part of protecting health more broadly.

This story draws on original reporting from Medical Xpress.