Exposure to air pollution before birth could increase the risk of cerebral palsy for babies, warns a study conducted at the University of Ottawa.
The risk was slightly higher for boys than for girls, but the difference was not statistically significant, the authors note.
Specifically, baby boys were at higher risk of cerebral palsy if they were exposed to high concentrations of PM2.5 particles during the first and second trimesters, and baby girls during the third trimester.
PM2.5 particles are so fine that they can lodge deep in the lungs and even enter the bloodstream, becoming a chronic source of inflammation.
“It has been observed that exposure to air pollution, particularly to PM 2.5 during approximately the second trimester of pregnancy, could increase the risk of having a child who will be diagnosed with cerebral palsy before the age of 18,” summarized the author of the study, assistant professor Éric Lavigne of the School of Epidemiology and Public Health at the University of Ottawa.
Only fine particles PM2.5 were associated with an increased risk of cerebral palsy. No such association was found in the new study with nitrogen dioxide or ozone particles.
PM2.5 particles can have a natural origin (such as forest fires) or human origin (such as combustion from factories or engines).
This study, the authors point out, is in line with previous work that has found an association between exposure to air pollution and a greater risk of neurodevelopmental disorders such as autism spectrum disorders and attention deficit hyperactivity disorder (ADHD).
Other studies have also found a higher prevalence of neurodevelopmental problems in boys than in girls, which is consistent with the data in the new study.
This difference between boys and girls remains to be elucidated, admit the authors of the study.
“The underlying mechanism of this male predominance and the sex difference in susceptibility windows warrant research to understand the influence of genetic, hormonal and environmental factors,” they write.
However, the researchers speculate that boys and girls may be more likely to develop different forms of cerebral palsy, which could reflect “different periods of vulnerability in utero.”
Air pollution, they say, could interfere with brain development at a crucial time.
“Myelination, which begins in the first trimester and is closely linked to white matter disorders such as cerebral palsy, appears to be the most susceptible to damage by particulate pollution,” they highlight among their hypotheses.
Additionally, Lavigne recalled, animal experiments have shown that exposure to air pollution can lead to inflammation of neurological systems.
An epigenetic cause could also be considered, he added, namely an influence of the environment on the way genes are expressed.
“It’s the accumulation of scientific evidence that points somewhat in the same direction,” said Mr. Lavigne. “It’s interesting to see that, in studies that focus on autism and ADHD, we sometimes see periods during pregnancy that are different from what we observed for cerebral palsy, so we see that it can be linked to different periods of brain development.”
Ultimately, he added, we see that “prenatal exposure to air pollution can clearly have long-term impacts.”
The new data could prompt doctors to advise pregnant patients to pay attention to air quality when they have to go outside, Lavigne said.
And from a regulatory perspective, he concluded, accumulating scientific evidence could eventually lead to “more restrictive enforcement of air pollution emissions regulations.”
The findings of the study were published in the medical journal JAMA Network Open.