"Both groups of women are dealing with children who need high levels of care-giving. But there is something about autism that is making a difference and adding stress and psychological distress to these mothers," said Annette Estes, lead author of a new study and associate director of the UW Autism Centre.
The research from the University of Washington's Autism Centre found no link between a child's decreased daily living skills and increased parental stress and psychological distress.
"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," Estes said.
"But it is not the hard work that is stressing the mothers. Our findings really pointed to the behaviour problems that can occur with autism.
"Children with autism had significantly higher levels of problem behaviours than children with developmental delay," she added.
These behaviour problems included such things as irritability, agitation, crying, inappropriate speech, and not being able to follow rules.
"Help in what we call family adaptive functioning is what we need to figure out in these cases. How to help families is important because high levels of stress and psychological distress can interfere with early identification of autism and interventions which are delivered by parents," she said.
"There's another good reason to do this: Parents who feel supported can better support their children," she added.