Autism Sex Differences Revisited: Swedish Study Finds Similar Prevalence Across Sexes but Delayed Diagnosis for Birth-Assigned Girls

Sweden's population-scale study on autism diagnoses across sexes challenges the long-held belief that autism is three times more common in boys. It finds the prevalence is fairly similar between sexes, but people assigned female at birth are diagnosed later, with a marked catch-up during adolescence and equal diagnoses by age 20. Flora Lichtman guides the discussion with Dr. Caroline Fefe, lead author and epidemiologist at Karolinska Institute, and later with Dr. Rachel Moseley, a psychologist and autistic adult, who share personal experiences and implications for treatment, education, and mental health. The conversation also touches on how diagnostic criteria and medical sexism may shape who gets diagnosed when, and why broadened understandings of neurodiversity matter for autistic women and girls.

Introduction and study context

In this Science Friday episode, Flora Lichtman presents a major epidemiological study from Sweden that tracks autism diagnoses in millions of individuals born between 1985 and 2022. The researchers, led by epidemiologist Dr. Caroline Fefe at the Karolinska Institute, examine how sex assigned at birth relates to autism prevalence and the timing of diagnosis. A central finding is that the overall prevalence of autism is fairly even across sexes, challenging the long-standing notion that autism is vastly more common in boys. The study also highlights a notable pattern: individuals assigned female at birth tend to be diagnosed later in life, with a rapid catch-up during adolescence. As the discussion unfolds, the hosts emphasize that the analysis uses sex assigned at birth, a nuance that shapes how results are interpreted and communicated.

Key findings by age and the timing of diagnosis

The conversation delves into the core results. Among children under 10, the sex difference remains relatively stable across the studied period, fluctuating roughly between 2.5 and 4 boys diagnosed for every girl. In contrast, when looking at older children, adolescents, and adults, the sex difference narrows substantially over time, with a distinct rise in the number of girls diagnosed during adolescence. By the time individuals reach 15 to 19 years old, the study shows a rapid convergence, and by age 20, the ratio approaches 1:1. These patterns indicate that while prevalence is similar across sexes, the path to diagnosis for birth-assigned girls often occurs later, likely due to differences in symptom presentation and diagnostic criteria.

"the Sex difference hadn't changed in children under 10 over that time" - Dr. Caroline Fefe, epidemiologist

Diagnostic criteria, masking, and gendered presentation

The episode shifts to how autism manifests differently in girls and how that influences diagnosis. Dr. Rachel Moseley, a psychologist and autistic adult, explains that autism has historically been described through male-centric criteria, which may have biased assessments toward stereotypical, early-onset presentations. She discusses masking—the tendency for autistic traits to be hidden in social contexts—which can mask differences in childhood and delay recognition until puberty and more complex social environments demand greater social navigation. The dialogue emphasizes that autistic girls often show equal social understanding but outward behavior that resembles their non-autistic peers, making detection harder in childhood and more apparent later in adolescence.

"One suggestion is that autistic girls are typically, uh, they may be slightly better at masking their autism" - Dr. Rachel Moseley

Discussion then turns to how diagnostic frameworks might evolve. Moseley advocates for language and criteria that align with neurodiversity, emphasizing a strengths-based approach that acknowledges differences as part of human variation rather than solely as deficits. This perspective could influence how clinicians discuss diagnosis, guide supports, and frame strengths alongside challenges.

From missed diagnoses to lived experiences

The conversation foregrounds the human impact of missed or late autism diagnoses. Moseley shares how missing a diagnosis can lead to long-standing self-blame, difficulties in school and employment, increased risk of abuse or exploitation, and heightened mental health challenges. She notes that improving diagnosis, particularly for girls and women, is linked to suicide prevention and overall well-being. The discussion also includes personal narratives from Moseley about her own diagnostic journey and the relief and validation that comes with a formal autism diagnosis, along with broader societal implications for education, healthcare, and family life.

"autism is markedly underdiagnosed in people assigned female at birth" - Dr. Rachel Moseley

Implications and next steps

Towards the end of the episode, the guests reflect on the need to extend research beyond birth assignment, acknowledging the presence of transgender and non-binary identities in autism research. They discuss potential future directions, including integrating register data with neurodiversity-informed criteria, and the importance of communicating nuanced findings in a way that reduces stigma while promoting access to timely supports. The episode closes with a broader call to recognize autistic people as a natural part of human diversity, with a spotlight on the ways we can minimize harm and maximize well-being through better diagnostic practices and inclusive understandings of autistic strengths.

"the diagnostic criteria are updated to reflect what we now know about neurodiversity" - Dr. Rachel Moseley