A groundbreaking study has found that exposure to air pollution during pregnancy may alter the structure of the developing fetal brain, even in pregnancies that appear otherwise healthy.
The research, led by the Barcelona Institute for Global Health (ISGlobal), analyzed over 700 pregnancies and provides the most detailed look yet at how pollutants like nitrogen dioxide (NO₂), fine particulate matter (PM2.5), and black carbon may impact fetal brain development.
Published in The Lancet Planetary Health, the study examined data from 754 mother-fetus pairs enrolled in the Barcelona Life Study Cohort (BiSC) between 2018 and 2021.
Using neurosonography — a specialized ultrasound — during the third trimester of pregnancy, researchers measured brain structures and compared them against estimated exposure to air pollution across three “microenvironments”: at home, at work, and during commuting. The exposure estimates were generated using hybrid models combining real-time environmental data and geolocation tracking via mobile apps.
The findings revealed subtle but significant structural changes in the fetal brain linked to higher pollution exposure, especially during the second and third trimesters — key periods in brain development. Increased levels of NO₂, PM2.5, and black carbon were associated with larger volumes of brain cavities containing cerebrospinal fluid, such as the lateral ventricles and the cisterna magna.
Researchers also observed a wider cerebellar vermis — the region of the brain involved in motor control — and a shallower Sylvian fissure, which may signal delayed brain maturation.
“These findings suggest that even low levels of air pollution — well within legal limits in many cities — can subtly affect how the brain is formed in utero,” said Dr. Payam Dadvand, senior author and ISGlobal researcher. “During mid to late gestation, the fetal brain enters a critical phase, making it particularly vulnerable to environmental stressors like pollution.”
Although the brain changes observed fell within the normal range of development, researchers stressed their relevance at the population level. “The differences may seem small individually, but when seen across hundreds or thousands of children, they could reflect a broader public health concern,” said Laura Gómez-Herrera, co-lead author of the study.
Clinicians involved in the study emphasized the urgent need for awareness and education about environmental risks during pregnancy. “We’re now seeing clear evidence that environmental exposures can influence brain development even when everything appears normal on the surface,” said Dr. Elisa Llurba of Hospital de Sant Pau and Dr. Lola Gómez-Roig of BCNatal-Hospital Sant Joan de Déu, co-authors of the study.
Still, the research team cautioned that more studies are needed to understand the long-term significance of these findings. “At this point, we can’t say whether these changes are reversible after birth or what their implications might be for future neurodevelopment,” said Dr. Jordi Sunyer, senior co-author.
While many questions remain, the evidence is mounting that air pollution has consequences far beyond respiratory health. “This study reinforces the need for stricter air quality regulations, especially in urban areas,” said Yu Zhao, co-lead author and researcher at ISGlobal.
As cities across the globe grapple with worsening air pollution, this research highlights the pressing need to protect pregnant women from environmental harm — not just for their health, but for the healthy development of future generations.
Read the full study here: https://doi.org/10.1016/S2542-5196(25)00093-2
