Children conceived through in vitro fertilization (IVF) are twice as likely to have autism as those conceived without assistance, a new study has found.
Assisted reproductive technology (ART) includes any type of fertility treatment where the egg and the sperm are handled outside of the body, including IVF, artificial insemination and surrogacy.
During IVF - the most popular ART treatment - more than one egg is harvested and fertilised, which can lead to multiple births.
The study was published online in the American Journal of Public Health.
The results aren't as damning as they first appear, though, with no proven cause-and-effect link. "The risk of autism appears to be largely modifiable by restricting IVF to single-embryo transfer," said lead researcher Peter Bearman, a professor of social sciences at Columbia University in New York City.
"There is an association between IVF and autism, but when we control for the characteristics of women who are more likely to use IVF, for example, age and social status, this association is lessened significantly," he said.
The study included nearly six million children born from 1997 to 2007. After taking into account factors such as mother's education and multiple births, the increased risk was seen only for mothers under 35, the researchers said.
Though the causes of autism are not known, environmental, biologic and genetic factors likely play a role, the agency says. In 2013, a parliamentary report estimated that one in 160 Australian children has ASD.