The study from UC Davis looked at more than 500 autistic children in California and compared them to the same number of children who did not have autism. Researchers found that the risk of autism and other development delays was 60 percent higher among those born to mothers who were obese, hypertensive or diabetic.
"If obesity is a risk factor for autism, now scientists have to explain why, what is it about obesity that puts children at risk? Is it the high levels of sugar in the blood, high levels of insulin or the chronic inflammation that you can sometimes see in people who are obese," said Dr. Richard Besser.
The U.S. Centers for Disease Control and Prevention in Atlanta estimates that one in 88 American children has autism - that's up from 1 in 110 children in 2006.
Obesity is also on the rise in the U.S., affecting more than one-third of American adults.
But medical experts - including the authors of the study - say there may not be enough information just yet to say whether the two are connected.
"If you're pregnant and you're obese, I wouldn't lose sleep over this study. I think the chances that if you have obesity it will cause autism in your child are yet unproven," Besser said.
Dr. Tom Frazier of Cleveland Clinic emphasizes that mothers who really want to be healthy, and want that for their children, need to pay attention to their own health.
More than a billion dollars have been spent on autism research in the last 10 years, but in many cases, they've been "association" studies, which don't prove direct cause and effect.
Some new studies being conducted this year are specifically targeted at genetics and the role that may play in the very complex puzzle of autism.