The proportion of females diagnosed with autism in the state of North Carolina has increased steadily over a 20-year period, which likely reflects greater societal knowledge of how autism may manifest differently in females. This is a key finding of a recent report, “Are the diagnostic rates of autistic females increasing? An examination of state-wide trends,” published online in January 2024, in The Journal of Child Psychology and Psychiatry.   

The study was conducted by a team of UNC researchers led by Clare Harrop, PhD, a Faculty Fellow at the Frank Porter Graham Child Development Institute (FPG), Assistant Professor in the Department of Health Sciences, and member of the UNC TEACCH Autism Program (UNC TEACCH). Her UNC TEACCH team member colleagues on this paper were: Assistant Professor and FPG Faculty Fellow Brianne Tomaszewski, PhD; Graduate Student Claire Klein; Research Manager Elena Lamarche, MPH; and Executive Director and FPG Faculty Fellow Laura Klinger, PhD. Orla Putnam, a fourth-year doctoral student in the Speech and Hearing Sciences program at UNC and a member of Harrop’s lab, is also a coauthor.

Autism has historically been considered a predominantly male diagnosis. But more recently, there has been consensus that autistic females are underdiagnosed or misdiagnosed. Suggested reasons for this variation in diagnostic rates include the presence or absence of co-occurring intellectual disability (ID), since females diagnosed with autism in childhood have been found to have higher rates of ID compared with males. In addition, there is debate over whether diagnostic practices and assessment, which have used males as the norm for decades, are suitable for females.

The study examined sex and age-related diagnostic trends in more than 20 years of statewide data from UNC TEACCH diagnostic clinics to address whether the rate of females diagnosed with autism have increased over the past two decades and whether the age of diagnosis for females has changed during this period. Data from 13,080 individuals were included in the initial analysis, with 10,247 autistic individuals in the final sample.

Individuals were seen at UNC TEACCH clinics for diagnostic evaluations led by a clinical psychologist between January 2000 and December 2021. These evaluations included a caregiver interview to gather developmental history and information on autism symptoms and a standardized evaluation of autism symptoms, followed by scoring of the Childhood Autism Rating Scale. A behavioral observation was also conducted.

The team focused on three research questions:

• Are more autistic females being identified over time?
• Has the age of diagnosis lowered over time for females relative to males?
• Have the number of late-diagnosed females increased over time?

Since the goal of the study was to characterize statewide trends in diagnosis by assigned sex at birth—which functions as the independent variable in this study—the researchers selected four dependent variables related to study participants: year of official diagnosis; DSM version at the time of diagnosis; age of official diagnosis; and intellectual disability status.

“Our statewide data shows that more females are making their way into our clinics, however their age of diagnosis remains higher, suggesting more work needs to be done,” says Harrop. “One reviewer described this dataset as ‘precious’ and it truly is – our team has begun to look at profiles of males and females in our dataset and we hope to continue to look at diagnostic trends over time.”

The team found a steady increase in the proportion of females being diagnosed with autism, with a faster increase in females relative to males over the same period. But females were consistently diagnosed, on average, 18 months later than males and were more likely to be “late diagnosed,” which the team defined at age 13 or older. As the authors note, while the increase in diagnostic rates for females is encouraging—and suggests an increase in both social and clinician knowledge of autism in females—younger females are consistently not diagnosed at the same rate as males.

The team also cautions that clinicians need to be aware of gendered norms and expectations when assessing females who have been referred for an autism diagnosis. This is needed to ensure access to appropriate supports and a sense of identity are available to females with autism. Many treatments have been created focusing on males with autism, but these approaches may not consider the needs of females. The team encourages future research into the data to interrogate whether the behavioral profile of females receiving a diagnosis has changed over time.

“Our statewide data shows that more females are making their way into our clinics, however their age of diagnosis remains higher, suggesting more work needs to be done,” says Harrop. “One reviewer described this dataset as ‘precious’ and it truly is – our team has begun to look at profiles of males and females in our dataset and we hope to continue to look at diagnostic trends over time.”