By Jenifer Goodwin HealthDay Reporter

FRIDAY, May 4 (HealthDay News) -- If a woman smokes during pregnancy, it may increase her child's risk of high-functioning autism, a new study suggests.

But the raised risk was slight, experts said. And researchers found no association between maternal smoking and more severe forms of autism.

What the findings suggest is that although autism spectrum disorders share many of the same symptoms, subtypes of the disorder likely have many different genetic and environmental causes that vary from person to person and by type of autism, explained study author Amy Kalkbrenner, an assistant professor in the University of Wisconsin-Milwaukee Zilber School of Public Health.

"We know 'autism spectrum disorders' is an umbrella term. What we're showing is the response to a environmental toxin may differ by the subtype of autism a child has," Kalkbrenner said.

The study was published online in the journal Environmental Health Perspectives.

Kalkbrenner and her colleagues examined data on maternal smoking from birth certificates of nearly 634,000 U.S. children born in 11 states in 1992, 1994, 1996 and 1998. That data was compared with information on 3,315 children aged 8 and under diagnosed with an autism spectrum disorder from the U.S. Centers for Disease Control and Prevention's Autism and Developmental Disabilities Monitoring Network.

About 13 percent of the mothers smoked during pregnancy, and 11 percent of the mothers of kids with an autism spectrum disorder smoked during pregnancy, the investigators found.

According to the study, kids born to moms who smoked during pregnancy had about a 25 percent increased risk of having high-functioning autism, such as Asperger's syndrome. However, the results did not reach statistical significance.

Nor was smoking a clear risk factor for autistic disorder (a more severe form of autism).

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Prenatal Smoking Linked to High-Functioning Autism in Kids