Abstract
Later autism diagnosis is associated with risk for mental health problems. Understanding factors related to later autism diagnosis may help reduce mental health risks for autistic people. One characteristic associated with later autism diagnosis is female sex. However, studies often do not distinguish sex assigned at birth and gender identity. Gender diversity may be more common in autistic relative to neurotypical people, and autism is more common in gender-diverse populations. We studied age at autism diagnosis by sex assigned at birth, gender identity, and gender diversity (gender-diverse vs cisgender) status, separately. We studied three separate autistic samples, each of which differed in how they were diagnosed and how they were recruited. The samples included 193 persons (8.0-18.0 years) from a research-recruited academic medical center sample; 1,550 people (1.3-25.4 years) from a clinic-based sample; and 244 people (18.2-30.0 years) from a community-enriched sample. We found significant differences in the clinic-based and community-enriched samples. People assigned female sex at birth were diagnosed with autism significantly later than people assigned male at birth. People of female gender were diagnosed significantly later than people of male gender. Gender-diverse people were diagnosed significantly later than cisgender people. Sex assigned at birth, gender identity, and gender diversity may each show unique relationships with age of autism diagnosis. Differences in how autistic people are diagnosed and recruited are important to consider in studies that examine sex assigned at birth or gender identity. More research into autism diagnosis in adulthood is needed.