New data has emerged from a California study of over half a million children that indicates that it may be the birth spacing of children, and not the age of parents, that plays the biggest role in a child's risk for developing autism.

The study, published in the journal Pediatrics, found that children born less than two years after their siblings were more likely to have an autism when compared to those born after at least three years.  In fact, the smaller the birth spacing between kids and the greater the likelihood of the later child being diagnosed with autism.   

For their study, researchers looked at the various levels of autism and factored other risk factors for autism, such as age of parents in to account but still found the strongest link between autism and birth spacing.

Interestingly, government numbers indicate that closely spaced births are on the rise, from 11 percent of all births in 1995 to 18 percent in 2002.  This could be the missing link behind autism's recent rise in prevalence.  Check out this video of the lead author, Dr. Peter Bearman of Columbia University, discussing the recent rise in autism.

Is it a case of parents being more observant with a second child (it's easier to notice delays when compared to an older child who hit milestones just a few months before)?  Or are there biological factors at work?  That is still unclear.  But these new findings, if they can be replicated, may give pediatricians and parents more information about how to prevent autism.