TIME magazine's article reporting on the study distinguishes between increases due to increased awareness and diagnoses versus increases due to an underlying increase in the condition.
Previous studies looking at a narrower population of youngsters have suggested that as much as 40% of the rise in autism cases might be explained by broader diagnostic definitions and by heightened awareness of the condition. But that still leaves 60% of the increase unaccounted for. "Most scientists believe there is something more than just awareness and a broadening definition that is responsible for the rise," says Dr. Gary Goldstein, president of the Kennedy Krieger Institute in Baltimore. "We are seeing some fraction of the increase that is probably due to more cases of autism."
TIME goes on to provide to specify some of the possible causes, focussing on the mother:
Since autism is generally diagnosed before age two, most scientists believe the factors that contribute to ASD occur during pregnancy, or in the months immediately following birth. A pregnant mother's advanced age might be one such influence, along with certain behavioral and environmental exposures she or her newborn baby may experience — any combination of which could be interacting with their particular genetic makeup to promote ASD. Isolating the most causative culprits will be a challenge, say autism experts. "There is so much stuff out there, whether it is diet or infection," says Goldstein. "We could make a list but it's got thousands of things on it."
The Wall Street Street Journal cites Catherine Rice, the CDC scientist who is the study's lead author, on the possible environmental factors leading to the increase:
Dr. Rice also said she couldn't rule out an actual increase in the number of autistic children. Research is under way into possible environmental factors, including vaccinations, household products and diet, as well as genetics, for potential causes, she said.
The Wall Street Journal also cites a source for the possibility that the age of the fathers may be a factor :
Philip Levy, president of YAI Network, a New York-based nonprofit that serves people with disabilities, including autism disorders, said the report confirmed that autism is "a continuing national health crisis." He added that some societal factors were helping to increase the risk of diagnosis. "With fathers in particular, there's a stronger correlation that has been made between older fathers and autistic children," Mr. Levy said.