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Autism and Air Pollution: Understanding the Effects of Pollution on Pregnant Women

Adding invaluable insight into what can cause a woman to give birth to a child with autism, a recent Harvard study has found a direct causal link between inhaling smog from vehicles or smoke stacks and autism. While previous studies have suggested that such a correlation might exist, the pregnant women in the study who lived in the most-polluted areas were up to two times more likely to have a child with an autism spectrum disorder (ASD), compared with those who lived in the least-polluted areas.


Part of what the Harvard study has expanded upon and provided greater insight into is when and where pregnant women are the most vulnerable, namely during their third trimester if they inhale elevated levels of microscopic airborne particles that are released by power plants, fires, and automobiles. The higher and more prolonged exposure resulted in a far greater risk.


According to Marc Weisskopf, the report’s senior author and associate professor of environmental and occupational epidemiology at the Harvard School of Public Health, “We found an association that was specific to pregnancy and especially to the third trimester, identifying a window, which might shed a light on processes that are happening that can lead to autism.”


By identifying the third trimester as the period when pregnant women are most at risk, researchers were able to draw a correlation between exposure to harmful pollutants and the fact that majority of neuronal growth occurs during the final three months of a pregnancy, a period when brain activity can be most affected. In contrast, the study found no association between autism and air pollution before or early in pregnancy, as well as after the child’s birth.


This increased understanding of how a person’s environment can affect the development of an unborn child might also provide insight into the fact that autism diagnoses are on the rise. The most recent data from 2010 indicating that as many as one in sixty-eight children are now diagnosed with some degree of autism spectrum disorder, a drastic rise from a 2000 study that found diagnoses in one in 150.


The Harvard study included children of 116,430 women that participated in the Nurses’ Health Study II, beginning in 1989. The researchers collected data on where the women lived while pregnant and the levels of air pollution present. They then compared the prenatal histories of 245 children with autism spectrum disorder to 1,522 normally-developing children, all born from 1990 to 2002.


By identifying a direct causal relationship between one’s environment and its effects on the development of a child, researchers have reasserted the importance of further studying other ways the environment can have an impact on increasing the prevalence of autism. While genetics still holds a key to understanding particular factors that lead to autism, this study reinforces the belief that genetics alone do not hold the answer to better exploring what causes autism. Exposure to certain pollutants and chemicals that are both man-made and occur naturally within nature play an equally important role in expanding scientists’ understanding of autism and their ability to provide expecting parents with concrete advice on what things to avoid during pregnancy. It is certainly a promising step forward to curtailing the rise in autism diagnoses.