Autism might be just as common in females as in males, according to a study published on Wednesday that counters prevailing estimates of the disorder's prevalence.

While the neurological and developmental condition is known to be more common in boys at younger ages, the study found a clear catch-up effect among adolescent girls, the researchers reported in The BMJ.

The findings highlight a need to investigate why autism spectrum disorders are diagnosed later in females than in males, they said.

The prevalence of ASD has increased over the past three decades, with three males now diagnosed for every female. Most diagnoses are made in childhood by the age of 10.

To analyze diagnosis rates over the life course, researchers in Sweden and the United States tracked 2.7 million individuals born in Sweden between 1985 and 2022, from birth to a maximum of age 37.

Overall, 2.8% of individuals were diagnosed with autism at an average age of 14.

Diagnosis rates were highest among boys at ages 10 to 14 and among girls at ages 15 to 19.

By age 20, the male to female ratio had evened out at nearly 1:1, the researchers found.

These findings and other recent research suggest "current practices are failing to recognize autism in many women until later in life, if at all," patient advocate Anne Cary wrote in an accompanying editorial.

The study did not account for genetics or environmental factors or for other conditions associated with autism, such as attention deficit hyperactivity disorder and intellectual disability, which might have played a role in patients' diagnoses.

Still, said Dr. Rachel Moseley of Bournemouth University in the UK, who was not involved in the study, “this paper is timely and provides important support for what autism researchers have known for a long time" about a substantial gap in diagnosing autism in females.

The study’s extended follow-up of young people is essential, she added, because studies of children may miss autistic features which are already present in males but not yet visible in females.

The high male to female ratio has also been attributed to better social and communication skills among girls, making autism more difficult to spot.

“And what we know about undiagnosed autistic people is that being undiagnosed is often associated with severe difficulties and even suicidality - so underdiagnosis... should be of serious concern,” Moseley said. (Reporting by Nancy Lapid; editing by Michele Gershberg and Nia Williams)