Still, "we found that a history of infertility and use of ovulation-inducing drugs was significantly associated with an increased risk of having a children with an autism spectrum disorder," said Lyall, who noted that the findings are preliminary, involved a relatively small sample of women and needed to be confirmed by future research.
The autism risk was less pronounced among younger mothers who took fertility drugs, Lyall added. Among women aged 25 to 34, about 3.1 percent who had infertility and took fertility drugs had an autistic child, compared to 2.6 percent of women in that age group who didn't.
The study was to be presented on Thursday at the International Meeting for Autism Research in Philadelphia.
Another study to be presented at the meeting, this time by Israeli researchers, found that in vitro fertilization and pre-term birth were both associated with an increased risk of autism in offspring.
About 10.2 percent of 461 children diagnosed with an autism spectrum disorder were conceived using IVF, while about 3.5 percent of children in the general Israeli population are conceived that way, according to the study.
Moms who had IVF tended to be older, with a median age of 32.6 years compared to just under 31 years of age for mothers who didn't get IVF, the study authors noted.
Nearly 4 percent of the kids with autism were born prematurely, while nearly 5 percent had a low birth weight, compared to about 1 percent in the general population.
"Prematurity and low birth weight also adversely affect the child's functioning in adaptive skills," noted study lead author Dr. Ditza Zachor, who is director of the Autism Center at Assaf Harofeh Medical
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