Prenatal exposure to tobacco smoke has been suggested as a possible contributor to the development of autism spectrum disorders (ASD), but a recent population-based study spearheaded by researchers at Drexel’s School of Public Health indicates that the two may not actually correlate.

“We found no evidence that maternal smoking during pregnancy increases the risk of autism spectrum disorders,” says Brian Lee, an epidemiologist and assistant professor at the School of Public Health.

Lee led the Sweden-based study, which will be featured in an upcoming edition of the Journal of Autism and Developmental Disorders, with a team of international collaborators.

Researchers have believed environmental exposures–anything not heritable–are likely relavent to the etiology of ASD, and many have thought tobacco smoke was a possible cause because of known associations with behavioral disorders and obstetric complications.

In addition, past studies of maternal smoking and autism have shown mixed results, with neither proving nor disproving the correlation.

Lee and his colleagues searched Swedish national and regional registries, analyzing 3,958 children with ASD and a control set of 38,983 children born during the same time period who did not receive an ASD diagnosis.

They found that 19.8 percent of the ASD cases were exposed to maternal smoking during pregnancy, while 18.4 percent of the control group were exposed to maternal smoking. During unadjusted analysis, the rates show an association between maternal smoking and the odds of an ASD diagnosis.

However, once the analysis was adjusted for certain sociodemographic factors such as the parents’ income, education and occupation, the association disappeared.

The results of the study can help reassure mothers that the act of smoking during pregnancy was likely not responsible for their child’s autism, and as Lee explains, “crosses off another suspect on the list of possible environmental risk factors for ASD.”

Although maternal smoking does not seem to increase the risk of autism spectrum disorders, Lee says is important to note that smoking during pregnancy is still very unhealthy for mothers and developing babies.