Smoking during pregnancy does not cause autism spectrum disorders (ASD) in children, finds a new study.
Researchers have considered a variety of chemical exposures in the environment during pregnancy and early life as possible contributing factors in the development of autism spectrum disorders.
Many have considered prenatal exposure to tobacco smoke a possible cause due to known associations with behavioural disorders and obstetric complications.
Past studies of maternal smoking and autism have had mixed results.
"We found no evidence that maternal smoking during pregnancy increases the risk of autism spectrum disorders," Dr. Brian Lee, an epidemiologist at Drexel's School of Public Health, who led the research in collaboration with researchers from Sweden's Karolinska Institute and the University of Bristol (Bristol, UK) said.
In the new study, Lee and colleagues analyzed data from Swedish national and regional registries for a set of 3,958 children with autism spectrum disorders, along with a control set of 38,983 children born during the same period who did not receive an ASD diagnosis.
Overall, 19.8 percent of the ASD cases were exposed to maternal smoking during pregnancy, compared to 18.4 percent of control cases.
These rates showed an association between maternal smoking and the odds of an autism spectrum disorder, in unadjusted analyses.
The report helps to reassure mothers who smoked during pregnancy that their behavior was not likely responsible for their child's autism,
Lee said, and "crosses off another suspect on the list of possible environmental risk factors for ASD."
However, he cautioned that smoking during pregnancy is still unhealthy for mothers and has other known risks for their children.
The study will appear in a forthcoming issue of the Journal of Autism and Developmental Disorders.