Girls and women on the spectrum are often overlooked, diagnosed with other conditions, and/or diagnosed later in life when compared to boys and men. There are various possible explanations for that. Probably more than one of them is at play in every situation. Some of the possible reasons are:
Girls on the spectrum are often omitted from research studies and less is known about them
The tools used to make a diagnosis are primarily based on research focused on boys and might not be a good fit for diagnosing girls.
Girls on the spectrum are referred less frequently for diagnosis
Once referred, ASD may be more difficult for clinicians to recognize in girls, especially in the absence of intellectual or behavioral problems
Gender stereotypes may lead to girls being missed
Girls on the spectrum might genuinely have better adaptation and compensatory strategies than boys
Girls may receive alternative diagnoses instead of ASD, such as intellectual disability, anxiety, ADHD, depression, etc.
Autism in girls and women looks differently in boys and men, and, consequently, they often do not get captured by the standard diagnostic procedures. The specific way autism manifests in girls and women is sometimes referred to as "female phenotype." Studies show that girls are less likely to have behavioral problems than boys. They also have better language and observational skills, are more socially attuned and have more emotional issues than boys.
Girls on the spectrum might have the following qualities:
Strong language skills
Look “less autistic” because they are observing, copying and mimicking people
Can have early speech development that masks social and communication difficulties
Can have solitary but not collaborative imaginative play
Can initiate, but not maintain, friendships
Systematizing (e.g., creating a manual of) social behaviors
Can be chatty using learned behaviors, scripts, and mimicking
Less rigid than boys
Have more social difficulties than boys
Restrictive interests are more socially acceptable
Get exhausted from regular activities
Need control and are bossy in relationships
Making multiple social faux pas, being direct and blunt
Having extremely high standards for friends, for example, demanding extreme loyalty
Can have "clingy" attachments to selected persons
Poor judgment -- the inability to predict the consequences of actions and read hidden agendas can result in bad choices
Girls who have average to above-average cognitive skills use their intelligence and sharp observational skills to hide their differences. The strategy of hiding autism-related challenges is called masking, or camouflage. There is no single definition of what camouflage is. I liked how it was defined in one research study as "The difference between how people seem in social contexts and what’s happening to them on the inside."
Both women and men use camouflage, but girls and women are better at hiding their difficulties and use camouflage more than men because they might be more motivated to fit in. They can successfully avoid anyone noticing their struggles, while simultaneously avoiding interventions and supports that could provide them with adaptive and social skills that could help them function better in the world.
Because of these difficulties in identification, autism should be considered for every girl who is "young for her age,' socially awkward and has sensory differences. Diagnosticians need to be familiar with the "female phenotype" and alert to the signs of camouflaging. A diagnosis might require in-depth qualitative assessments that go beyond superficial skills and mannerisms and include investigation of reasons behind behaviors.
For example, in one research study, it was observed that at recess autistic girls weave in and out of groups of peers in the same way that the typical girls do. It turned out, however, that the autistic girls were rejected by their peers and went to the next group in hopes of being able to join in, only to be rejected again and try another group. Meanwhile, typical girls flitted successfully between different group conversations. To a less attentive observer, the autistic girls' behavior could have appeared typical.