When one pregnancy is immediately followed by another within one year of birth, researchers report there could be an increased risk of autism in the second child. The study revealed that children born two to three years after their older sibling are also at increased risk, though the risk is lower.

Researchers looked into the health records for more than 650,000 children born in the state of California. The children were born to mothers who had given birth to an older sibling within the previous 12 months. According to the findings, the second child was at risk for autism three times higher than that of their peers. Children born in the second year had twice the risk. By the third year, the risk of autism was down to 26% more likely, though that risk is significant.

Threat of autism does not seem to be concentrated with second children. In families where the third child was born within one year of the second child, an increased risk of autism was also noted. Researchers and experts have no idea why these children are at greater risk but some believe it has something to do with the female body not being given enough time between pregnancies to recover.

Source: Keely Cheslack-Postava PhD, Andy Shih PhD. Pediatrics. February 2011.