How early can you — and should you — diagnose autism?

Claire McCarthy, MD

Senior Faculty Editor, Harvard Health Publishing

Autism is common. According to the most recent data from the Centers for Disease Control and Prevention (CDC), 1 out of every 59 children has been diagnosed with autism. That’s a marked rise from 2000, when only 1 in 150 children had been diagnosed with autism.

There is a lot we don’t know about autism, such as exactly what causes it or why it is becoming more common. But one thing we do know is that the earlier we start treating it, the better. Communication and social skills are built very early. We have our best chance of improving things if we work within that natural window. That’s why there has been a steady push toward making the diagnosis as early as possible.

It is not easy for parents to hear that their child has, or might have, autism. Even when there are worries about the child’s development, it is natural to hope that a child is just a late bloomer, or a bit quirky. And indeed, some children are late bloomers, or quirky, or have an entirely different problem with their development. So how early can you reliably diagnose autism?

What does research on autism tell us?

A recent study focused on this question. Researchers looked at more than 1,200 toddlers who had at least two developmental evaluations between 12 and 36 months. Less than 2% of the toddlers initially thought to have autism were subsequently thought to have normal development. And on the flip side, 24% initially thought to not have autism were then later diagnosed as having it. So while the picture is not always clear at first, once the diagnosis is made, it usually sticks.

At what age can the diagnosis be reliably made? At 12 to 13 months the “diagnostic stability” of the autism diagnosis — meaning the degree to which it was certain and stuck — was about 50%. This went up to 80% by 14 months, and 83% by 16 months. This makes sense if you think about the development of a toddler. At 12 months, they are just starting to say words, respond to commands, and interact with others. So a child who isn’t reliably doing those things would be cut some slack. But by 18 months, all those skills should be solidly in place, raising alarm bells about a child who doesn’t have them.

Which treatment strategies may help children with autism?

The main treatment for autism is called applied behavioral analysis (ABA). This is a behavioral program that breaks actions and behaviors down into small steps. It encourages positive behaviors and discourages negative behaviors. Other treatments include occupational therapy, sensory integration therapy, and strategies to improve communication, such as using pictures that children can point at to let caregivers know what they want.

Here’s the thing: ABA and the other treatments are helpful for children with developmental problems, no matter what their cause. There is no downside to doing them even if the child ultimately is found to have a different problem — or no problem at all. They are good for the child with autism, the child with a language disability, or a late bloomer. Yes, it’s hard for parents to hear a diagnosis of autism. But there is much reason for hope when it comes to autism, and we should never waste time when a child needs help.

The CDC’s Act Early campaign has a whole host of resources to help parents and caregivers know if a child is developing normally, or if there might be a problem. If you think there is a problem, ask for help. You have nothing to lose, and everything to gain.

Follow me on Twitter @drClaire

Related Information: Harvard Health Letter


  1. Ashley Bolen

    My son was diagnosed with ASD and ADHD at age 4. I knew there was something wrong around 2 1/2 to 3 years old but didn’t want to come to terms with it. He hit all his milestones at a reasonable time until it came to talking. He probably didn’t actually start talking until he was 3 and started a Pre-K program twice a week. Then he started speech therapy at the local elementary school where they determined he had a developmental delay plus a speech delay. Where we live it is close to impossible to get therapy as soon as you can. So we had to wait until this summer to start occupational therapy. He has overcome so many speed bumps in the past year. He is in kindergarten now and doing great. He’s considered and inclusion student but they had to back him out of the class and reintroduce him because he became overwhelmed walking into his classroom with 20 sets of eyes staring at him. Now he goes to his developmental delay therapist first then to his classroom where he is slowly transitioned into it then pulled out to go back to his DDT and sent to an inclusion teacher to try and help him be included every day all day. He does speech therapy and occupational therapy twice a week at the school. Parents when a phycologist diagnosis your child with ASD please don’t panic and be scared. I was that mom that broke down and cried in the Dr office. They are going to be ok. School systems have classes and programs to help these babies adjust! My son LOVES numbers and can count extremely high for a kindergarten and add some pretty big numbers together.

  2. Asma

    Hi, very good article thanks for sharing.
    You are excellent blogger

  3. Alex Gaston

    Thank you for this blog/site of Harvard. Much appreciated.

  4. Dewang Kapadia

    At which age, which vaccination is given ? Any studies ?

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