From Autism Speaks
October 16, 2014
Findings in North Carolina mirror those in California, with autism rates highest when pollution exposure occurs during third trimester.
A new study adds to the growing body of evidence linking autism to air-pollution exposure during late pregnancy. In particular, the researchers looked at exposure to particulate matter – the kind of pollution associated with traffic.
The findings, by researchers at the University of Wisconsin-Milwaukee, appear this week in the journal Epidemiology.
In all, the investigators analyzed recordings of particulate levels near the homes of 77,500 children in North Carolina and 87,000 children in California. The measurements began before conception and continued, every three weeks, through pregnancy and the child’s first year of life.
The researchers then compared the timing and level of pollution exposure for around 1,000 children who went on to develop autism with that of the other children in the study.
Effect Strongest in Third Trimester
They found that air pollution had the greatest effect on autism rates if the exposure occurred during the last three months of pregnancy. Autism rates were around a third higher among children in this group. By contrast, the study found no significant increase in autism rates when pollution exposures occurred either earlier in pregnancy or after birth.
These findings, by researchers the University of Wisconsin-Milwaukee, mirror those of two earlier studies looking at particulate pollution and autism rates in Northern California.
The finding that only late-pregnancy pollution exposure had a strong effect on autism rates is also consistent with theories linking autism to altered brain-network development during the final months of pregnancy.
Including two geographic regions enabled the researchers to look at differences in climate, seasonal weather patterns and the regional make-up of pollutants. For instance, the researchers found that, in North Carolina, pollution exposures were highest for children born in summer. In California, exposures were highest for children born in fall and winter.
Translating Findings into Action
“Our confidence that air pollution during pregnancy is a risk factor for autism grows with each replication of this finding,” comments epidemiologist Michael Rosanoff, Autism Speaks director for public health research. (Rosanoff was not directly involved in the study.)
“Now we can focus on biology and what puts some mothers at higher risk than others – and more importantly, what public health practices can reduce this risk.”
Further study is also needed to understand how specific pollutants affect brain development during crucial prenatal periods.