Rates of autism were found higher among the children of teen moms and among children whose parents have relatively large gap between their ages. The largest-ever multinational study also found higher risk for older parents to have children with autism. More than 5.7 million children in five countries were analyzed by researchers for the study.

Findings of the study have been published in the journal Molecular Psychiatry. Co-author Michael Rosanoff, Autism Speaks' director of public health research, said that the research is distinct from many previous studies conducted on autism and parental age.

"By linking national health registries across five countries, we created the world's largest data set for research into autism's risk factors. The size allowed us to look at the relationship between parents' age and autism at a much higher resolution - under a microscope, if you will", said co-author Michael Rosanoff, Autism Speaks' director of public health research.

Co-author Sven Sandin said that the risk associated with autism has a lot to do with parental age, but the majority of children born to older or younger parents will go through normal development process.

Dr. Sandin, a medical epidemiologist, is affiliated with the Icahn School of Medicine at Mount Sinai, in New York, and Sweden's Karolinska Institutet.

The study was conducted with the aim of determining whether or not autism risk is related to advancing maternal or paternal ages.

Autism rates were found 66% higher among children born to dads over 50 years of age than among those born to dads in their 20s.