The connection was long hypothesized, but never actually proven

Jan 16, 2012 12:46 GMT  ·  By

Scientists from the Drexel University say that smoking during pregnancy is not directly linked to the development of autism spectrum disorders (ASD) in children, despite what other studies have shown.

Investigators with the research team conducted a study on this potential correlation on a large population sample from Sweden, and found that, if a connection between smoking and autism is there, it is indeed an indirect one.

For a long time, the development of ASD was considered to be the result of mothers exposing themselves to various chemicals and particles during the pregnancy. Naturally, the environment is the primary source of such particles.

In this line of thought, smoking indeed appeared to play a part in triggering these disorders, the most notable of which is autism. However, the new investigation proves that is not the case, setting experts back in their quest to find the root cause of these conditions.

The new study should not be interpreted as saying that smoking is not harmful to fetuses. The habit does cause behavioral disorders and obstetric complications in infants, the researchers group explains.

The thing is the alleged connection between smoking and the development of autism in newborns has never been entirely proven. All studies conducted on this issue have thus far yielded mixed results.

“Past studies that showed an association were most likely influenced by social and demographic factors such as income and occupation that have associations with both the likelihood of smoking and with the rate of autism spectrum disorders,” says Dr. Brian Lee.

In the new investigation, researchers included data on 3,958 children who were diagnosed with ASD, and cross-referenced these information with records covering 38,983 kids who did not receive such a diagnostics, PsychCentral reports.

“We found no evidence that maternal smoking during pregnancy increases the risk of autism spectrum disorders,” says Lee, who was the leader of the new study. He is as an assistant professor at the Drexel University, and also an epidemiologist at the university's School of Public Health.

His team conducted the research together with colleagues from the Karolinska Institute, in Sweden, and the University of Bristol, in the United Kingdom. The researchers determined that 19.8 percent of ASD children were exposed to prenatal smoking. But so were 18.4 percent of children in the control group.

Statistically speaking, what this means is that a fetus' risk of developing ASD after birth is minimal, even if the mother smokes during pregnancy. Details of the new study appear in the latest issue of the Journal of Autism and Developmental Disorders.