Inducing labor doesn't appear to increase the baby's odds of autism, a new study suggests.

Researchers examined data on more than 1.3 million births in Sweden and found about 3.5% of babies born after induction were diagnosed with autism by age 20, compared with 2.5% of other infants. This translates into a roughly 19% greater risk of autism with induced labor, which is statistically significant.

But when researchers took a closer look just at sibling pairs with one baby that arrived after induction and another that didn't, they no longer found any link between induced labor and autism risk.

The results from nearly 700,000 siblings suggest that any elevated autism risk associated with labor induction is actually due to other factors such as genetics or medical issues experienced by individual women, said lead study author Dr. Anna Sara Oberg of Harvard University in Boston.

"The association observed between unrelated individuals may be a result of confounding factors, and not a causal effect of labor induction on the risk of autism spectrum disorder," Oberg said by email.

Oberg and colleagues reviewed data on all live births in Sweden from 1992 to 2015. Overall, about 11% of these deliveries were induced, the researchers reported online July 25 in JAMA Pediatrics.

Labor induction was more common when mothers were older, obese, hypertensive, or diabetic.

The mother's country of origin, education level and smoking status early in pregnancy didn't appear to impact whether they would have an induced labor.

One limitation of the study is that it didn't examine various types of labor induction, which can include a variety of medications and procedures to help labor begin and progress, the authors note.

The findings from the current study also run counter to a large 2013 study of U.S. babies that did link labor induction to a greater risk of autism, Oberg noted.

More research is needed to explore how different types of induction or various reasons for induced labor may influence the odds of babies developing autism, Oberg said.

Still, findings from the current study should be reassuring for parents, said Dr. Bryan King, a researcher at Seattle Children's Hospital and the University of Washington who wasn't involved in the study.

"These investigators were able to take advantage of a very large population database to look within families and compare the risk for siblings who were induced versus those who weren't, thus better controlling for other genetic and environmental risks," King said by email.

It's possible that any greater risk of autism seen with induction is actually due to the medical reasons induction was needed, and not to the medication used to help labor progress, said Dr. Daniel Coury, a researcher at Ohio State University in Columbus and Nationwide Children's Hospital who wrote an editorial accompanying the study.

"The odds are very positive that the product of an IVF pregnancy or an induced labor is going to be a healthy child," Coury said by email. "The great majority of children with autism have not been the product of an induced labor; we still don't know all the causes of autism."

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JAMA Pediatrics 2016.