Couples who have a child diagnosed with autism appear significantly less likely to have additional children, researchers say, no matter how many kids they already have.

In a study looking at health records on more than 55,000 California families — 19,710 of which included a child with autism — researchers found that parents’ reproductive behavior was similar in both groups of families until the time children with autism typically start to show symptoms of the disorder. At that point, however, a third of families with a child on the spectrum stopped having more kids.

The trend of what’s known as “reproductive stoppage” held true whether the child with autism was the family’s first or later born, the study found.

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“While it has been postulated that parents who have a child with ASD may be reluctant to have more children, this is first time that anyone has analyzed the question with hard numbers,” said Neil Risch of the University of California, San Francisco, who worked on the study which was published online Wednesday in the journal JAMA Psychiatry.

The finding that many families choose to stop having children after learning that their son or daughter is on the spectrum may mean that current estimates on the odds of having a second child with autism could be unreasonably low, researchers said.

When reproductive stoppage was taken into account, the study found that the odds of having a second child with autism rose to 10.1 percent for full siblings, an increase over the 8.7 percent estimate found when families who stop having children are not factored in.

The study did not examine why parents of children with autism are more likely to stop having kids, but researchers said it could be due to concerns about having another child with the disorder or that parents feel they are unable to care for additional children after having one on the spectrum already.