Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterized by persistent challenges in social communication and interaction, alongside restricted, repetitive patterns of behavior, interests, or activities. The term “spectrum” reflects the wide variation in how these characteristics present. Recognizing developmental differences early is important, as interventions initiated in infancy or toddlerhood can enhance long-term developmental trajectories. Since a formal diagnosis of ASD is typically made around two years of age, understanding subtle variations in development from zero to 24 months allows parents and clinicians to seek early support. This article focuses on behavioral and communication patterns that may signal a need for further developmental evaluation during a child’s first two years.
Vocalization Patterns and Crying Myths
A common question is whether infants who develop ASD cry less or not at all, but crying is a highly variable behavior. Infants with ASD do cry, though the acoustic properties of their cries may differ from those of neurotypical infants. Studies suggest that the cries of infants later diagnosed with ASD can have an atypical pattern, sometimes featuring a higher pitch or a wider frequency range. This difference in sound may lead to caregivers responding to the crying in different ways, potentially affecting the early parent-child communication loop.
More reliable early indicators often lie in the development of pre-linguistic sounds, such as cooing and babbling, which are the building blocks of speech. Typically developing infants begin canonical babbling—the production of consonant-vowel combinations like “ba-ba” or “da-da”—around six to 10 months. Infants later diagnosed with ASD often show significantly lower rates of this canonical babbling compared to their peers. This difference in the frequency and type of sounds is known as lower volubility.
Vocalizations are also often not used in a responsive, communicative manner. Neurotypical infants engage in vocal turn-taking, where a sound from the parent elicits a sound from the baby, creating a conversational rhythm. Infants with ASD may show reduced or absent participation in this back-and-forth vocal exchange. The sounds they make are less likely to be directed toward a caregiver or accompanied by face-gazing, indicating a difference in social motivation.
Differences in Early Social Engagement
Differences in social engagement are among the most consistent and earliest signs of ASD, often emerging within the first year of life. Eye contact is a primary tool for early social connection. A lack of sustained eye contact or an active aversion to looking at faces can be noted as early as six months. This reduced visual attention to social stimuli can affect how the infant processes emotional information and bonds with caregivers. The reciprocal social smile, where an infant smiles specifically in response to a caregiver’s smile, may also be absent or infrequent.
A child’s response to their name is another important developmental milestone that often presents atypically. While a six-month-old may not respond consistently, a lack of response to their name by nine to 12 months is considered a reliable early predictor. Parents may worry about hearing loss, but the concern is rooted in a difference in social attention rather than a physical inability to hear. This unresponsiveness suggests a reduced orientation toward social cues.
Joint attention, the ability to share a focus on an object or event with another person, is a foundational social skill that is frequently delayed or absent. This behavior is typically demonstrated when a child looks at a toy, then looks back at a parent to ensure the parent is also looking. Infants with ASD often do not follow a parent’s gaze or pointing gesture to share interest. Instead of pointing to share enjoyment, a toddler with ASD may take a parent’s hand and use it as a tool to access an object, known as hand-leading, without making eye contact.
Sensory Processing and Repetitive Movements
Infants who develop ASD often process sensory information—sight, sound, touch, taste, and smell—in an atypical manner, showing either hypersensitivity (over-reaction) or hyposensitivity (under-reaction) to stimuli. A hypersensitive infant might become distressed by everyday sounds, such as a vacuum cleaner or a dog barking, leading them to cover their ears. They may also show an intense aversion to certain clothing textures or resist being held or cuddled because the touch feels overwhelming.
Conversely, a hyposensitive infant may seek out intense sensory input to register the sensation. This can manifest as an excessive tendency to mouth non-food objects, stare intently at bright lights, or not react appropriately to pain or extreme temperatures. These differences in sensory processing can make it challenging for the child to regulate emotions and interact comfortably with the surrounding environment.
Repetitive behaviors, or stereotypies, are a core feature of ASD that can appear in the first two years of life. These movements often involve the body, such as hand-flapping, body rocking, or stiffening and posturing the hands and fingers. The frequency, intensity, and persistence of these behaviors distinguish them as potential signs of ASD. Repetitive engagement with objects is also common, including spinning wheels, lining up toys in a rigid way, or unusual visual inspection of objects.
Developmental Milestones and Seeking Professional Guidance
Noticing differences in early development involves observing two distinct patterns: a lack of acquisition or a loss of skills. In many cases, infants later diagnosed with ASD exhibit a lack of acquisition, meaning they never develop a particular skill within the expected timeframe, such as not babbling by 12 months or not using single words by 16 months. For a subset of children, a developmental regression occurs, where they temporarily acquire skills in areas like language or social interaction, only to lose them suddenly, typically between 18 and 24 months.
If a parent observes any persistent signs, consulting a pediatrician is the appropriate first step. Pediatricians utilize standardized tools, such as the Modified Checklist for Autism in Toddlers, Revised (M-CHAT-R), during well-child visits at 18 and 24 months to screen for potential concerns. This screening process is not a diagnosis but a way to identify children who would benefit from a comprehensive evaluation.
When a screening indicates a higher likelihood of ASD, the pediatrician can provide a referral for a comprehensive developmental evaluation by a team of specialists, such as a developmental pediatrician or a child psychologist. Early identification is beneficial, as it allows a child to access intervention services, which can begin before a formal diagnosis is finalized. These services, which may include speech or occupational therapy, are tailored to the individual child and support the development of communication and social skills.