Rates of autism in girls and boys more equal than previously thought, research finds

Rates of autism among girls and boys may be more equal than previously thought, according to a large Swedish study which found differences in timing of diagnosis.

The study of health records from 2.7 million individuals tracked from birth to up to 37 years of age found a show a clear female catch-up effect during adolescence in autism diagnoses.

Writing in the BMJ, the researchers said a high male-to-female diagnosis ratio of around four to one had been suggested to be related to better social and communication skills among girls which makes autism more difficult to spot.

But no research had looked at this trend over the life-course, they noted.

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The analysis, which looked at a national register of people born between 1985 and 2022 of which autism was diagnosed in 78,522 (2.8%) of individuals at an average age of 14.3 years.

They found that diagnosis rates increased with each five-year age interval throughout childhood, peaking at 645.5 per 100,000 person years for male individuals at age 10-14 years and 602.6 for female individuals at age 15-19 years.

It meant that while boys were more likely to be diagnosed in childhood, by the age of 20 years the ratio between males and females was almost the same.

The analysis did not consider other conditions associated with autism, such as ADHD nor did it look at shared genetic and environmental conditions like parental mental health.

They concluded: ‘These findings indicate that the male to female ratio for autism has decreased over time and with increasing age at diagnosis.

‘This male to female ratio may therefore be substantially lower than previously thought, to the extent that, in Sweden, it may no longer be distinguishable by adulthood.’

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But they added the findings highlight the need to investigate why female individuals receive diagnoses later than male individuals.

Dr Monique Botha, associate professor in social and developmental psychology, at Durham University, said autism is not a male condition, ‘yet girls struggle to get a diagnosis in a timely or robust manner’.

Dr Laura Hull, research fellow at the University of Bristol Medical School, said the findings support the idea that historically autism has been under-diagnosed in girls and women.

It is important to note there may have been other factors, such as co-occurring mental health conditions, influencing diagnosis timing which were not measured, she added.

‘Accounting for the whole picture of individuals being assessed is important considering the high rates of conditions such as anxiety, depression, and eating disorders in this group.

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‘Diagnostic rates are still changing and it remains to be seen whether the male-to-female ratio will continue decreasing, will stabilise, or even will increase again as we continue to “catch up” with diagnosis of girls and women who were missed earlier in life.’

A version of this article was first published by our sister title Pulse