Women who smoke during pregnancy could be more likely to have a child with high-functioning autism, say researchers.
'It has long been known that autism is an umbrella term for a wide range of disorders that impair social and communication skills,' said lead author Professor Amy Kalkbrenner from the University of Wisconsin-Milwaukee.
'What we are seeing is that some disorders on the autism spectrum, more than others, may be influenced by a factor such as whether a mother smokes during pregnancy.'
Smoking danger: Pregnancy is known to increase the risk of miscarriage
Prof Kalkbrenner and her colleagues looked at a population-based study comparing smoking data from birth certificates of hundreds of thousands of children from 11 states to a database of children diagnosed with autism.
They found that 13 per cent of mothers whose children were identified as having an autism spectrum disorder at the age of eight had smoked during pregnancy.
WHAT IS AUTISM?
These children were more likely to have high-functioning autism such as Asperger's Disorder, which has a less severe impact.
'The study doesn't say for certain that smoking is a risk factor for autism,' Prof Kalkbrenner says.
'But it does say that if there is an association, it's between smoking and certain types of autism.'
Other risks of smoking during pregnancy are well known.
Every time a pregnant woman smokes, she restricts the oxygen delivered through the placenta that's essential for a baby's healthy growth and development.
The habit increases the risk of miscarriage, stillbirth and premature birth.
Resulting babies are twice as likely to die from cot death. They also have a higher risk of suffering asthma and ear infections.
Despite this an estimated 13 per cent of pregnant women smoke in England and the U.S.
The Centers for Disease Control and Prevention in the U.S recently released data that suggested one in 88 American children have an autism spectrum disorder.
Prof Kalkbrenner said it made environmental studies like hers 'even more timely.'
Because autism involves a broad spectrum of conditions and the interplay of genetics and environment is so complex, no one study can explain all the causes of autism, she adds.
'The goal of this work is to help provide a piece of the puzzle. And in this we were successful.'
The study was published by the journal Environmental Health Perspectives.
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