Autism Diagnosis Rates Nearly Equal Between Males and Females by Early Adulthood, claims study

A new study published in the British Medical Journal showed that as the age at diagnosis has increased, the male to female ratio for autism spectrum disorder (ASD) has declined over time. The long-standing 4:1 male-to-female autism ratio is considerably declining, according to recent studies.

There is a "female catch-up" impact throughout adolescence, even if males receive diagnoses earlier. Incidence rates are now close to parity by age 20, indicating that earlier discrepancies were caused more by masking and diagnostic bias than by actual biological differences. Thus, this study investigated the changes in the male to female ratio in ASD diagnoses over a 35-year period, providing temporal trends in diagnosis (incidence rate), the male to female ratio, and the cumulative male to female ratio (cMFR) specific to age cohort.

This study was a prospectively gathered birth cohort study that was population based. Between 1985 and 2020, there were 2,756 779 live births listed in the Swedish medical birth registry. Using incidence rate ratios and related two-sided 95% confidence intervals, age-period cohort analysis examines relationships between ASD and sex, calendar period, age at diagnosis, and birth cohort.

ASD was identified in 78,522 (2.8%) of the 2,756 779 people who were born in Sweden between 1985 and 2020 at the end of follow-up (2022). Throughout childhood, the incidence rate of ASD rose with every five-year age interval. It peaked in 2020–2022 at 645.5 (per 100,000 person years) for the male cohort at age 10–14 and 602.6 for the female cohort at age 15–19. After that, it started to decline.

Between 1985 and 2020, the age-specific incidence of ASD rose for every calendar year and birth cohort. As the age at diagnosis increased and, for those above ten, by calendar period, the male to female ratio declined. By the age of 20, the cumulative male to female ratio for the incidence of ASD was 1.2 for the last year of follow-up in 2022.

According to additional projections of these trends, by 2024, the cumulative male to female ratio would equalize at age 20. Overall, the results, which are based on an examination of the Swedish population over a period of more than 35 years, show that both the MFR and the number of ASD diagnoses have declined over time. 

Source:

Fyfe, C., Winell, H., Dougherty, J., Gutmann, D. H., Kolevzon, A., Marrus, N., Tedroff, K., Turner, T. N., Weiss, L. A., Yip, B. H. K., Yin, W., & Sandin, S. (2026). Time trends in the male to female ratio for autism incidence: population based, prospectively collected, birth cohort study. BMJ (Clinical Research Ed.), 392, e084164. https://doi.org/10.1136/bmj-2025-084164