Parental and psychological stress is higher in mothers of children with autism, U.S. researchers say.

The study, published in the journal Autism, finds these moms fared worse than moms of children with developmental delay.

"Both groups of women are dealing with children who need high levels of care giving," lead author Annette Estes of the University of Washington in Seattle says in a statement. "But there is something about autism that is making a difference and adding stress and psychological distress to these mothers."

The researchers were surprised to find no link between decreased living skills in a child and increased stress related to parenting or psychological distress -- defined as stress or nervousness about life in general.

"This finding was counter-intuitive," Estes says. "If a child has more needs in getting dressed and in other daily living skills, that means the parents are working harder and seemingly would be under stress. But it is not the hard work that is stressing the mothers. Our findings really pointed to the behavior problems that can occur with autism. Children with autism had significantly higher levels of problem behaviors than children with developmental delay."