Many girls face years-long delays in receiving autism diagnoses, with many not diagnosed until adulthood, new research has shown.

Diagnosing autism – which impacts more than 5million adults and over 2million children in the US – can be difficult because there is no definitive medical test, such as blood draws or MRI scans, to diagnose the disorder. 

Doctors instead must look at the child or adult’s developmental history and behavior to make a diagnosis. 

In the recent study by Epic Research, researchers reviewed records from more than 338,000 patients who received their first autism spectrum disorder diagnosis between 2015 and 2024.

They found that the median age at autism diagnosis declined slightly from seven years of age in 2015 to six years in 2024, thanks to improved understanding of the condition. 

However, they discovered that male patients are increasingly diagnosed earlier with the median age at diagnosis dropping from seven years in 2015 to five in 2024. 

This contrasts with the trend for females, with the median age of diagnosis remaining around the age of eight over the same period.

Digging into the data further, the researchers discovered among male patients diagnosed with autism in 2024, 44 percent were under age five, compared to 34 percent for females.

Many girls face years-long delays in receiving autism diagnoses, with many not diagnosed until adulthood, new research has shown (stock image)

They said that this indicated that more than half of these female patients were diagnosed later than age five and ‘might have benefitted from earlier diagnosis’.

They also found that the proportion of female patients diagnosed as adults (aged 19 plus) was 25 percent in 2024, while 12 percent of males were diagnosed with autism as adults in the same year.

Dr Brian Harris, a behavioral health and development physician at Orlando Health who was not involved in the study, says the diagnosis gap between girls and boys is largely due to the traditional diagnosis model.

Offering an explanation as to why the gap exists, he says: ‘Despite the benefits of early diagnosis and intervention, most autistic children are not diagnosed until they begin school, by which time they and their peers are expressing rigid gender-based stereotypes. 

‘That may be why the behavior of a loud and rowdy autistic boy catches attention while that of a quiet girl expressing subtler symptoms may not.

‘In other words, the model we’ve been using to diagnose ASD is a male model, but we are changing that. 

‘Specialists at all levels are being trained to recognize symptoms in boys and girls because a diagnosis provides clarity, enhances understanding, and opens access to support, resources and services that can be life-changing.’

Early research from the 1960s and 1970s estimated autism affected just two to four out of every 10,000 children, but the condition was poorly understood at the time.

While diagnosis rates have steadily climbed over the years, they were already much higher by 2000, when the CDC reported a prevalence of 1 in 150 children aged eight or younger.

This then jumped to one in 44 in 2018, one in 36 in 2020, and one in every 31 children in 2022 – a rate of 32.2 per 1,000. 

By comparison, early studies from the 1960s and 1970s estimated autism rates to be as low as 1 in 5,000. 

Diagnosing autism can be difficult because there is no definitive medical test, such as MRI scans, to diagnose the disorder (stock image)

The most recent CDC report found wide geographic variation, with diagnosis rates ranging from roughly one in 100 in parts of south Texas to a striking one in 19 in San Diego. 

It also highlighted shifting demographic patterns: autism diagnoses were more frequent among Asian, Black, and Hispanic children than among White children — a trend first observed in the 2020 data. 

Researchers say the sharp rise in recent decades can be partially explained by improved screening, increased public awareness, and better access to services. 

While some blame an ultra-processed diet, chemicals and pesticides for the rise.

The average age for an autism diagnoses is five, though the vast majority of parents notice differences in their children, particularly around social skills, as early as two years old. 

Looking ahead, Professor Rinehart says more research needs to be done to better understand the autistic gait. 

This will be particularly beneficial to children so that treatment plans can be tailored for their individual movement styles as they develop.