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
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
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).
The researchers noted that the data used in the study may
underestimate the true prevalence of autism spectrum disorders
among mothers who smoke because lower-income kids are less likely
to be identified as having autism, and lower-income mothers are
also more likely to smoke during pregnancy.
When researchers did another statistical analysis that took into
account a suspected undercounting of kids with autism, the analysis
did suggest a statistically significant association between smoking
and high-functioning autism in offspring.
Alycia Halladay, director for environmental research for Autism
Speaks, said the research is consistent with prior studies that
have found either no association or only a mild association between
smoking during pregnancy and autism in children. What's interesting
about this paper is that it included data on large numbers of kids,
she added, and it hinted at differences in the contributing factors
for various types of autism spectrum disorders.
"It really supports the idea that there are multiple causes of autism, both genetic and environmental. When we talk about autism being one group or disorder, we really need to ensure we have these groups as well-defined as possible," Halladay said. "This is a very heterogeneous disorder."
There are multiple reasons why tobacco might raise the risk of
autism, Kalkbrenner noted. Tobacco can restrict oxygen flow to the
baby, while the nicotine is known to interact with the nervous
system and cross the placenta into the developing fetus. "There are
many potential biological pathways for which tobacco can harm the
developing baby," she said.
Autism is a neurodevelopmental disorder that's characterized by
problems with social interaction, verbal and nonverbal
communication and restricted interests and behaviors. An estimated
one in 88 U.S. children has the disorder, according to the CDC.
National Institutes of Health has more on autism.
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