There are various early signs of Autism Spectrum Disorder (ASD) that can be identified in children, this will differ based on a range of factors including age and severity of symptoms.
Due to its heterogeneous presentation, identifying the early signs of ASD can be challenging. We had a look at some of the research on the signs of ASD and how they may differ by age and gender.
- How Early Do Signs of ASD Appear?
- How Do I Know If My Child Is On the Autism Spectrum?
- What are the Signs of ASD in Children up to 6 Months Old?
- What Are the Symptoms of ASD Between 6-12 Months?
- What Are the Symptoms in Children Aged 1-2?
- Are There Differences Between Boys and Girls When Identifying Signs of ASD?
How Early Do Signs of ASD Appear?
There have been various studies seeking to identify when signs of ASD typically appear. A study in the Journal of the American Academy of Child & Adolescent Psychiatry  found that it was hard to detect any differences in behaviour of infants at 6 months old, however, when the infant reaches 12 months old, it was much easier to see significant differences in those with ASD and those without.
They also state that results from their study found that the ‘behavioural signs of autism are not present at birth…but emerge over time through a process of diminishment of key social communication behaviours’.
While current research suggests that individuals are born with Autism Spectrum Disorder, Parents may only become aware of the signs as the child becomes older and/or attends day care or preschool or may not report any signs or issues with the child’s behaviour they experience for a variety of reasons.
How Do I Know If My Child Is On the Autism Spectrum?
There are various signs, which may indicate ASD, these include deficits in social communication, visual attention and restricted and/or repetitive behaviours.
Social interaction and communication are a strong indicator of distinguishing autism in children. This can include limited ‘Pretend play, functional play, showing and reading parents’ facial expressions’ 
Children with ASD may be less likely to smile, respond to their name, sounds and people or objects moving around them in the same ways as typically developing children do.
It should be noted that signs will vary based on age, an outline of these variations are listed below.
A child with ASD may have difficulty maintaining eye contact or focusing their visual attention on social interactions similar to those of their peers. This can limit the child from accessing important early social interactions with others, as well as limit their development of early communication skills.
During a controlled study  children’s visual attention was recorded during two scenarios:
- Firstly, a play-based interaction with an examiner, and
- Secondly, where the examiner pretended to hurt themselves.
During the second scenario, the children who were later diagnosed with ASD continued to stare at the toy, rather than look at the examiner. The children who were not diagnosed with ASD displayed increased interest in the examiner following the examiner hurting themselves.
Restricted and Repetitive Behaviours
Restricted and repetitive behaviours may be present in a child with ASD. These may look different depending on the child, with some more common than others.
Repetitive behaviours may include hand flapping, lying down and rolling wheels close to eyes, looking out the corner of eyes and/or engaging loud non-functional vocalisations.
Restricted behaviours may include inflexibility to changes in routine or excessive interest in a particular topic or item. Often changes to routine or disruption to access to preferred items/activities can lead to problem behaviour (e.g., meltdowns).
It is noted, however, that some typically developing young children may develop some level of repetitive or restricted behaviours throughout their development. Contrary to their typically developing peers, however, these behaviours often impact the ability to learn and engage socially for individuals with ASD.
What are the Signs of ASD in Children up to 6 Months Old?
It is difficult to diagnose a child with autism when they are only 6 months old and it is rare that a professional would provide an ASD diagnosis at this age. However, research from Henry Massie , suggests that there are some signs that may be present at this age that could indicate ASD.
Signs of atypical development from birth to 6 months in children later diagnosed with ASD may include:
- Low muscle tone (e.g., difficulty with gross motor movements such as rolling over)
- Lack of responsiveness or attentiveness to people or things (e.g., does no smile or show excitement to parents or toys)
- Lack of anticipatory posturing on being picked up (e.g., raising arms to parent when being picked up
- Vacant, unfocused gaze
- Specific motor deviations (e.g., head lag when moving from laying down to sitting, facial palsy)
- Low mood (e.g., non-responsiveness to social games or interactions, excessive crying)
- Difficulty with sleep (e.g., difficulty falling to sleep or remaining asleep)
*These signs are not specific to ASD and may occur in children who develop normally or with other problems; however, they were more frequent in infancy films of children subsequently diagnosed with ASD than in control films of children who were not diagnosed with ASD.
What Are the Symptoms of ASD Between 6-12 Months?
Massie  also suggests early signs that could present in infants between 6-12 months, these may include:
- Showing excitement for no apparent reason
- Lack of interest in other people (e.g., does not track others movements or respond to others attempts to engage)
- Avoiding other’s gaze
- Repetitive behaviours: hand-flapping, rocking, spinning
What Are the Symptoms in Children Aged 1-2?
From ages 1-2 signs may become clearer and may include the following:
- Child doesn’t approach parents or familiar others
- Child keeps distance from parents or peers and prefers to play alone
- Facial expression that doesn’t convey intention or meaning
- Failure of typical language development 
- Increase in restricted or repetitive behaviours
Early identification of ASD allows for children to access early intervention services sooner. Research has shown that the younger children are when they access early intensive behavioural intervention and the more intensive the intervention is (e.g., minimum 20 hours per week), the more positive the outcomes.
Are There Differences Between Boys and Girls When Identifying Signs of ASD?
A study looking at children aged 18-36 months  in Tianjin, China found that the prevalence of ASD was 27.5 per 10 000, with a male to female ratio of 4:1. This often prompts the question, are boys are more likely to have autism than girls? Or is there another reason for this?
We know that the signs of autism in boys and girls may be similar, however a study  by Harwood and Kasari (2007) found that girls are able to ‘camouflage’ their symptoms by staying in close proximity to their peers, whilst more frequently changing activities. Engagement in these activities may mask their social challenges and so may not be picked up as early. This could possibly explain why we can see higher numbers of boys diagnosed with ASD.
In the same study , by comparison, boys with ASD tended to more often play alone which makes them easier to distinguish.
Parent reported concerns are another way we may see differences between girls and boys. For example, repetitive and restricted behaviour symptoms reported by parents were less likely to present in girls than boys , however, parent-reported symptoms such as emotional and behavioral problems made it more likely to result in a positive ASD diagnosis in girls than boys.
We are most likely to notice signs of ASD in children from around 12-18 months old, although symptoms can present sooner. Parents who are concerned that their child may be presenting with symptoms should speak to their doctor who can refer them to their local specialist for assessment. There are effective clinically proven programs that can support children with ASD and an early diagnosis is ideal.
- A Prospective Study of the Emergence of Early Behavioral Signs of Autism
- Prevalence and Early Signs of Autism Spectrum Disorder (ASD) among 18–36 Month Old Children in Tianjin of China
- Selective Visual Attention at Twelve Months: Signs of Autism in Early Social Interactions
- Signs of Autism in Infants: Recognition and Early Intervention
- The art of camouflage: Gender differences in the social behaviors of girls and boys with autism spectrum disorder
- Factors influencing the probability of a diagnosis of autism spectrum disorder in girls versus boys