The way parents decide to space having their babies is a personal choice, one dependent on how old they are, their work situations, their finances and how close in age they want their children to be. But now they may need to consider another factor: how it affects their kids’ risk of autism.

A new study published in the journal Pediatrics found a link between the number of years between first- and second-born children and the risk that the younger child will have an autism spectrum disorder (ASD). Specifically, researchers discovered that kids born less than two years after their older siblings and those born six or more years later were 1.5 to 3 times more likely to develop autism, which affects 1 in 68 children in the United States, according to the Centers for Disease Control (CDC).

The study authors analyzed the data for 45,000 babies born in a Northern California hospital between 2000 and 2008. They found that 1.2 percent of second children, or 577 total, were diagnosed with some form of autism, with those born less than two years later or more than six years later having an increased risk.

“That means if roughly one in 100 kids are born with autism, the odds jump to up to 3 in 100,” study co-author Lisa Croen, PhD, director of the Kaiser Permanente Autism Research Program in Oakland, Calif., told Yahoo Parenting.

The findings are in line with recommendations by the World Health Organization (WHO) that children be spaced at least two years apart to avoid premature birth, low birth weight and other health problems. Though researchers found a link between spacing children and autism, they didn’t explain the reason behind it.

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