Air Pollution Linked to Increased Risk of Postpartum Depression

Women exposed to higher levels of air pollutants such as nitrogen dioxide (NO₂) and inhalable particulate matter (PM₁₀) during pregnancy may have an increased risk of postpartum depression. That’s according to research from The Keck School of Medicine of the University of Southern California (USC).

The study, published in Science of The Total Environment, examines the long-term effects of environmental factors on maternal mental health.

Exposure to air pollution increases risk of developing a mental health condition

Around 10% of pregnant women and 13% of those who have just given birth experience a mental health condition. In developing countries, these numbers increase to 15.6% and 19.8% respectively. Symptoms of pregnancy-related depression include feelings of sadness, impaired concentration and a loss of ability to function normally. In severe cases, mothers may commit suicide, or be unable to take care of their child, impacting the infant's growth and development.

While all mothers are vulnerable to developing mental health disorders during and after pregnancy, some may be more susceptible. Factors such as stressful life events, poverty, exposure to violence and a genetic predisposition can all increase a woman's risk.

Recent epidemiological studies have indicated that exposure to air pollution may also contribute to an individual's risk of developing a mental health condition. Airborne particulate matter (PM) can increase neuroinflammation and oxidative stress in the brain – which might influence structural and functional changes associated with mental disorders. Animal studies have highlighted that PMs can induce responses similar to anxiety and depression in mice.

Dr. Tracey Bastain, an associate professor in the department of population and public health sciences at USC, and team are now researching how exposure to air pollutants – such as NO₂ and PM₁₀ – during pregnancy may impact a mother's risk of developing a mental health condition.

“While this is still an emerging area of research, evidence is increasing that exposure to air pollution during pregnancy is an important risk factor for postpartum depression in the first year,” said Bastain.

“NO₂ is generally considered a near roadway pollutant and has a complex chemistry relationship with ozone which generally leads to lower ozone levels in larger urban areas.  PM₁₀ is generally considered to be a regional pollutant but is high in urban areas and has a variety of sources from traffic particles to pollens to wildfire smoke,” said Bastain.

Mid-pregnancy period a critical window for long-term maternal mental health

The longitudinal study followed 361 women from the start of pregnancy to 3 years postpartum. The participants were recruited by the Maternal and Developmental Risks from Environmental and Social stressors (MADRES) Center for Environmental Health Disparities at the Keck School of Medicine, which predominantly follows Hispanic/Latino families in Los Angeles from low-income areas. Data was collected on the mother’s depressive symptoms at 12-, 24- and 36-months post-partum. These data were then compared with daily residential pollutant concentrations, which were estimated from monitoring data and calculated weekly average levels.

Women exposed to elevated levels of NO₂ between weeks 13 and 29 of pregnancy had a 3.86 times higher risk of developing postpartum depression for up to 3 years. Similarly, those with increased exposure to PM₁₀ between weeks 12 and 28 faced a 3.88 times greater risk.

“This effect was not explained by postpartum air pollution during the first year after childbirth, nor subsequent pregnancies, which were both surprising. Our results are quite compelling that the mid-pregnancy period is a critical window for long-term maternal mental health outcomes,” said Bastain.

“This period is frequently marked by a reduction in nausea and fatigue that are common during the first trimester, which may promote increased outdoor activities and a higher level of physical activity that may result in a greater dose of inhaled pollutants,” said Bastain. “In the second trimester, there is also substantial uterine growth and dynamic shifts in cardiometabolic processes, including increased cardiac output, blood volume, heart rate and pulmonary circulation. These are all critical processes for supporting the developing fetus but may make a pregnant woman more susceptible to environmental exposures.”

Post-partum depression rates may be higher than originally perceived

Overall, 17.8% of the participants experienced depressive symptoms after one year, 17.5% after 2 years and 13.4% after 3 years. 

“We showed that rates of postpartum depression in the first 12 months are higher than national prevalence estimates and that these outcomes are quite persistent beyond that period, which is not something that most health care providers focus on,” said Bastain.

“That’s quite important – there’s probably more postpartum depression out there than even our national prevalence data are showing,” she added.

“We hope that these findings will shed light on the importance of considering the environment during pregnancy for long-term women’s health and well-being,” Bastain concluded.

Bastain and her colleagues plan to continue studying the long-term effects of air pollution and chemical exposure on the health of mothers and children. Their research will also explore the biological processes underlying various health risks.

Reference: Hu Y, Niu Z, Eckel SP, et al. Prenatal exposure to ambient air pollution and persistent postpartum depression. Sci Total Enviro. 2024;953:176089. doi: 10.1016/j.scitotenv.2024.176089

About the interviewee:

Dr. Theresa (Tracy) Bastain is an associate professor in the department of population and public health sciences at The Keck School of Medicine of the University of Southern California (USC). Dr. Bastain received an AB in Psychology from Princeton University and a MPH from the Johns Hopkins Bloomberg School of Public Health. She completed doctoral and postdoctoral training in Epidemiology at USC. Dr. Bastain’s research interests include understanding and mitigating the effects of environmental exposures in early life and during critical periods (e.g., pregnancy) on maternal and health outcomes with an emphasis on mental health outcomes in women and neurodevelopment in children.