Is it Autism or Global Developmental Delay?

For families and pediatricians of toddlers, one area of confusion can be differentiating between a child who is developmentally delayed and one who is showing symptoms of autism. A child who presents with areas of developmental delay, particularly in communication, is commonly referred for an autism evaluation. What makes this challenging is the significant overlap in symptoms between the two groups.

While developmental delays are common in children with autism, they are not themselves a core feature of autism or part of the diagnostic criteria. Instead, autism is defined by differences in social communication and interaction, along with restricted or repetitive patterns of behavior.

So how do we tell these two groups apart?

Behaviors that may appear in both groups

First, here are some examples of behaviors or skill deficits that may be observed in both children with autism and children with developmental delay.

• Verbal communication delays - One area of delay that can be seen in both children with developmental delay and those with autism is communication. Delayed communication may contribute to a diagnosis of global developmental delay. In autism, however, the defining concern is not simply delayed language but differences in social communication. Delayed language can impact many other areas of development. Limited verbal communication may result in less social engagement or fewer opportunities for interaction. In a child with only a communication delay, social engagement often improves significantly once language skills begin to develop (especially with appropriate speech intervention). In autism, social communication differences typically persist even as language develops.

• Social-communication differences - Children with developmental delay may show difficulty with things like social withdrawal, fewer attempts at social interaction, or less use of gestures and other nonverbal communication behaviors. In these cases, their social skills often appear consistent with their developmental level, similar to what might be expected from a younger child. In children with autism, these social communication skills appear unusually weak even when their developmental level is taken into account.

• Motor stereotypies - These are repetitive movements such as hand-flapping, which many people associate with autism. However, repetitive movements are also common in typically developing infants and young toddlers. Because of this, these behaviors alone are not very helpful in distinguishing between typically developing toddlers, children with developmental delay, and children with autism. What matters more is the frequency, intensity, and how much these behaviors interfere with social interaction or play.

• Intense interests or attachment to unusual objects - This is something I have encountered frequently when evaluating toddlers for autism. It is not uncommon for toddlers to develop strong attachments to a wide range of items that become their “comfort object.” A favorite toy car, pillow, toy sword, or marker may become extremely important to a two-year-old, just as much as a blanket or stuffed toy. Toddlers also commonly develop highly specific interests, such as a favorite television show or character. While these strong interests are typical in young children, they become more unusual if they are unusually rigid, highly restricted, or persist well beyond the toddler years.

• Adaptive functioning - Immature adaptive functioning is often seen in both children with autism and children with global developmental delay. One difference that can help distinguish between the two is the pattern of delays. Children with developmental delay alone often show relatively even delays across areas such as cognition, communication, daily living skills, and socialization. Children with autism may show a more uneven developmental profile, with relative strengths in some areas and more significant weaknesses in others.

What helps clinicians tell the difference?

Fortunately for evaluators like myself, there is a growing body of research that helps clinicians determine which behaviors and skill levels best distinguish between children with autism and those with developmental delay.

In general, symptoms related to autism such as social communication differences and restricted or repetitive behaviors, must be greater than what would be expected based on the child’s developmental age. For example, if a child is 4 years old but functioning developmentally closer to a 2-year-old level, the clinician asks whether the child’s social communication skills resemble those of a typical 2-year-old, or whether they appear significantly weaker even when that developmental level is taken into account.

Research suggests that social communication differences are particularly helpful in distinguishing between the two groups.

Areas clinicians pay close attention to

• Eye contact - Toddlers with autism often show limited or unusual use of eye contact during social interaction. In a child with developmental delay, eye contact typically appears more expected for their developmental level.

• Joint attention - Toddlers with autism may show less pointing to share interest, less following of others’ gaze or pointing, and less showing of objects to share interest with others. In toddlers with developmental delay, pointing and showing objects are usually present but may appear more consistent with their developmental level rather than their chronological age.

Children with developmental delay generally show more social interest, respond socially to others (even if in less mature ways), and seek engagement with others more often than what may be seen in children with autism.

The role of comprehensive evaluation

Ultimately, clinicians distinguish between developmental delay, autism, and cases where both are present by considering the child’s developmental level and comparing autism-related symptoms to that level.

This determination is made through a comprehensive evaluation, which typically includes:

• a detailed developmental history

• developmental testing (including cognitive level)

• adaptive functioning assessment

• standardized direct observation instruments involving structured play observation (such as the ADOS-2)

Having an accurate diagnosis, whether developmental delay, autism, or both, is crucial for understanding how best to support the child and their family.

For families, my advice is simple: never hesitate to ask questions, dig deeper, and voice your concerns about your child’s development.

References:

Olson, H. E., & Spence, S. J. (2024). Differential diagnosis of autism spectrum disorder and other neurodevelopmental disorders. Pediatrics, 153(2), e2023062151. https://doi.org/10.1542/peds.2023-062151

Sperandini, C., et al. (2025). Differentiating autism spectrum disorder and global developmental delay in preschoolers: Overlapping profiles and diagnostic challenges. Journal of Autism and Developmental Disorders.