Oxytocin and prostaglandins are used to start or speed up labor but the study doesn't identify specific medications.
The strongest risks were in boys whose mothers had labor started and hastened. They were 35 percent more likely to have autism.
Among girls, autism was not tied to induced labor; it was only more common in those born after labor was accelerated; they were 18 percent more likely to have the developmental disorder than girls whose mothers had neither treatment.
Autism affects about 1 in 88 U.S. children. Symptoms may involve communication problems including avoiding eye contact and unusual repetitive behavior including arm-flapping. Causes are uncertain but experts believe it probably results from a combination of genetics and other factors. These may include mothers' illnesses and medication use while pregnant, fathers' age at conception, and problems affecting the fetus during childbirth — all suggested but not proven in previous research.
The study's biggest strength is bolstering the growing consensus that risks for autism occur before birth or soon after, said Dr. Byron King, director of Seattle Children's Hospital's autism center. He was not involved in the study.