Earlier this month, a prestigious medical journal, The Lancet, retracted a report that linked autism to a vaccine against measles, mumps and rubella. Autism is a complex disability that affects a person's ability to communicate and interact with others. There are many theories about what causes autism. The latest has to do with a mother's age.
Many women know that having a baby after 40 carries some risk. Cherri Cary was 40 when she gave birth.
"One of the concerns was Down syndrome," said Cherri Cary. "Another concern was pregnancy loss."
But Cary never thought her age could increase her child's risk for autism.
Her son Ben has been diagnosed with the disorder.
Researchers from the University of California looked at millions of parents. They found that women who gave birth after age 40 were nearly twice as likely to have a child with autism as a woman under 25.
But the increased risk is small. Only five percent of the increased risk is attributed to maternal age. Researcher Janie Shelton was the lead author.
"We know that it is a risk factor but we can't attribute the rise in autism to the shifting trend towards having children later in life," said Janie Shelton.
Older mothers are known to face increased risks for having children with genetic disorders, and genes are thought to play a role in the entire autism spectrum. This can include people with asperger's syndrome who are highly functioning.
"I have a third cousin who has asperger's, and a first cousin who has just PDD, autism," said Erica Romano.
Erica Romano has three children with autism.
The California researchers say a mother's age is not the only risk factor.
The study also found that the age of the father can play a role, although it is not as significant as the age of the mother.
From all accounts, autism seems to be on the rise throughout much of the world.
The Centers for Disease Control shows that the number of children with autism in the U.S. more than doubled between 2002 and 2006. About one child in 100 has a form of autism.
Some researchers dispute the steep rise in the numbers. Anthropologist Richard Grinker wrote a book about it.
"You can't really compare today's rates with the rates of 10 years ago, 20 years ago," said Richard Grinker. "Because they're apples and oranges. The concept of autism was very different in the past."
Parents and doctors are more aware of autism now which leads to earlier diagnosis. And the definition of autism has broadened so people with wide ranges of functioning are now diagnosed on the autism spectrum.
The latest study claims that parental age, by itself, does not cause autism, but it may be one risk factor and one more piece of the autism puzzle.