Parents who have children with autism are more likely to decide not to have more kids after seeing the symptoms of the disorder.

Based on a new study, parents of children with autism are around one-third less likely to have more children compared to those who do not have children with the disorder. The study found that it could be a reproductive decision. It has always been postulated that parents with autistic children are more reluctant to conceive more children but the study is the first to analyze the subject and confirm numbers.

The researchers identified children with autism spectrum disorder (ASD) born between 1990 and 2003 in California. During that period, 19,710 families were identified to have a first born. There were 39,361 individuals including siblings and half-siblings. There was also a control group of 36,215 families with 75,724 individuals who had no family member with ASD.

The reproductive behavior of parents was similar between those with and without children with ASD. However, the birth rates varied in the following years with families which had first born children with ASD having only a second child rate of 0.668 as that of those with no family member with ASD. Women who changed their partners had an even lower rate of 0.553 for a second child.

The confirmed numbers are important in calculating the likelihood that a couple's second child will be diagnosed with ASD after the first one had the disorder. The estimate risk used to be 8.7 percent but now that scientists factor in that many parents decide not to conceive again after a diagnosis, the number moves up to 10.1 percent.

"This study is the first to provide convincing statistical evidence that reproductive stoppage exists and should be taken into account when calculating the risks for having a another child with ASD," senior author of the study Neil Risch said. "These findings have important implications for genetic counseling of affected families."

The research also did not include stillbirths and miscarriages which may also affect the period it takes for a couple to conceive a child and their decision to bring more children into the world, but these factors will not be able to explain the findings alone.