How autism presents differently, is routinely underdiagnosed, and collides with menstruation
Autism is consistently described as inherently ‘male’, with a diagnostic ratio of 4:1, males to females, most often cited. However, recent evidence is pointing to the fact that women and girls are significantly underdiagnosed. Why? Girls and women are being missed, not because autism is rarer in them, but because it does not always look the way the textbooks were written to expect. They mask more, their intense interests get waved through as “normal” and the tools built to catch autism were built around boys.
On top of this, autistic women and girls have different experiences of menstruation and cycling life than neurotypical people. The experience of menstruation itself - smells, feelings of discomfort and disrupted routines - is particularly destabilising for autistic individuals. Recently, conditions such as endometriosis and PMDD have been shown to occur at higher rates in autistic women - adding more complexity to the picture.
In this blog, we will dive into the contested sexual dimorphism in autism and explain the differential experiences of menstruation that autistic women and girls may have.
The Sexual Dimorphism of Autism - Is it Really True?
The DSM-V states that autism spectrum disorder is diagnosed four times more often in males than in females, and this is the manual that clinicians use to inform diagnosis. But is this really true?
A recent systematic review and meta-analysis analysed 54 studies with over 13 million participants. When they screened for autism in the populations, the diagnostic male to female ratio landed more at the 3:1 mark, closing the gap significantly (1). A 2026 Swedish study went further, tracking autism diagnoses across 2.7 million people in a national register (2). In children aged 10 or younger the male to female ratio was the widest at approximately 3:1. However, after age 10, that gap all but disappeared, diagnostic rates evened out between males and females.
A quick look into the biological theories
Several biological theories try to explain a sex difference in autism, and none of them settles it.
The female protective effect proposes that females have greater genetic resilience, so they can carry more autism-linked genetic variants before crossing the threshold for a diagnosis. The Extreme Male Brain hypothesis, now widely regarded as dated, casts autism as an exaggerated version of a "male" brain, framing male brains as more systemising and female brains as more empathising, and links this to higher testosterone exposure in the womb (3). Autistic people are more likely to have had high prenatal testosterone exposure, which is the evidence usually offered in its support.
But the idea that male brains "systemise" and female brains "empathise" is hard to separate from old stereotypes dressed up as neuroscience. And when Lai and colleagues (2013) looked at the actual structural neuroanatomy of male and female autistic brains, they found significant differences between them, which opens up a very different possibility: that female autism is not a milder version of male autism at all, but a distinct presentation (4).
Is it Biology or Bias?
If the biology is this hazy, the more likely explanation for the diagnostic gap is not a real difference in how common autism is. It is that the instruments used to measure it were calibrated on boys, and embedded with assumptions rather than facts. Which raises the real question: does the male-to-female ratio differ because of underlying biology, or because of a skewed picture of what autism is “supposed” to look like?
The evidence points at the second.
Diagnostic Tools Built on Boys Miss Girls
A 2026 systematic review and meta-analysis examined the diagnostic tools in current use (5). The most prominent ones, ADOS, ADI-R and SCQ, were developed and validated on predominantly male samples. As a result, they lean heavily on externalising, disruptive or socially conspicuous behaviours, and they are far less sensitive to the internalising presentations more common in girls and women: emotional distress, social anxiety, interpersonal hypervigilance. Restricted interests in girls also tend to look socially acceptable, things like literature or animals, so they go unnoticed. On top of that, autistic girls and women mask, consciously or not, compensating for traits that would otherwise be flagged.
The sexual dimorphism in autism, then, may not be that autism is a male condition. It may be that female autism is actually different, and presents differently from the classical male picture that everyone was trained to look for. Here we are again: women being asked to fit a mould that was built for men. Better tools, ones designed around how autism actually shows up in girls and women, would give them what they have been denied: the chance to be seen, understood and believed.
The Exhausting Art of Fitting In (aka Masking)
A 2025 systematic review of 10 studies found that autistic girls and women are slipping through the cracks, not because they are “less autistic”, but they’re indeed better at hiding it (6). Using the Camouflaging Autistic Traits Questionnaire (CAT-Q), autistic women scored significantly higher on masking (suppressing outward autistic traits) and compensation (actively performing neurotypical behaviour). We built a diagnostic system that misses it, and a world that rewards that hiding. But it comes at a cost, because constant masking is exhausting, linked to higher anxiety, depression, burnout and social marginalisation. The authors themselves call for camouflaging to be built into how autism is diagnosed, not treated as a side note.
Menstruation Can Amplify Everything
We can’t speak about autistic girls and women at DITTO without mentioning the experience of menstruation.
The first study to centre autistic voices in menstrual health research out in 2018, titled "Life is Much More Difficult to Manage During Periods": Autistic Experiences of Menstruation. (Steward et al) (7). Autistic participants reported that menstruation significantly amplified their existing autism-related difficulties.
Periods can intensify existing sensory sensitivities in autistic people. Autistic individuals describe being sensitive to the smell of blood, and being more sensitive to noise, touch and visual stimuli when menstruating. Menstrual pain can become overwhelming for autistic individuals, making it hard to focus on anything else. Not only do physical experiences intensify, but emotional ones do too. Around menstruation, autistic individuals note difficulties in recognising, describing and managing emotions, and experiencing more anxiety and meltdowns.
These experiences of autistic women and girls often go unnoticed and unrecognised, leaving little support available. The paper recommends three things:
(1) Better menstrual education built specifically for autistic people, step-by-step, practical, and prepared in advance, since autistic respondents were less likely to pick up informal info from peers
(2) Clinician training to actually connect mood/behavior changes to menstruation in autistic patients, since that link is currently often missed and leaves severe symptoms untreated and unsupported
(3) A call for systematic research into the causes and impact of menstrual problems in autistic people, since almost none exists.
Autism, PMDD and Endometriosis
Autism also travels with comorbidities that relate to menstrual health. One study found that 21% of autistic women met the criteria for PMDD, compared with a control group of 3% of non-autistic women, though the exact figures vary between studies (8). That's not surprising once you consider what's already going on: autistic women already experience heightened sensory sensitivity and emotional regulation challenges. Premenstrual hormonal shifts can intensify these, and disrupt a sense of stability which is often crucial for coping, and can tip into heightened anxiety, shutdown and emotional dysregulation. The handful of studies emerging on this do suggest that screening for PMDD in autistic women who are struggling around this time in their cycle would be sensible. To make this happen, raising awareness of this evidence amongst healthcare providers is so important.
Some research also suggests autistic women may have around twice the rate of endometriosis (9). The mechanisms linking autism to either condition remain badly understudied, which is its own scandal given how much these conditions shape daily life. We have an article on neurodivergence and endometriosis here if you‘re interested in reading more.
The Takeaway
Autistic women and girls deserve to be recognised, supported and taken seriously, with care built around their actual experiences of life and of menstruation, not around a template made for someone else. For most of autism's history they have been forced into a male mould, and the cost has been chronic underdiagnosis and a shallow understanding of what female autism really is. Not to mention, conditions like PMDD and endometriosis that compound an already exhausting picture, remain largely unstudied and unscreened for despite emerging evidence on higher prevalence rates.
This has very much been a "who we were looking for, and how" problem. None of that is fixed by asking autistic women to explain themselves better. It's fixed by better tools, better research, and a willingness to ask why autism looks different in women instead of assuming it doesn't. Autistic women don't need to be more like the textbook. The textbook needs to catch up to them.
References
1. Loomes R, Hull L, Mandy W. What Is the Male-to-Female Ratio in Autism Spectrum Disorder? A Systematic Review and Meta-Analysis. Journal of the American Academy of Child & Adolescent Psychiatry, 2017; 56, 466-474
2. Fyfe C, Winell H, Dougherty J, Gutmann D H, Kolevzon A, Marrus N et al. Time trends in the male to female ratio for autism incidence: population based, prospectively collected, birth cohort study BMJ 2026; 392 :e084164 doi:10.1136/bmj-2025-084164
3. Szakal, C., and B. Crespi. 2026. “ Does the Extreme Male Brain Hypothesis of Autism Apply More to Females Than Males? A Systematic and Meta-Analytic Approach.” Autism Research 19, no. 4: e70198. https://doi.org/10.1002/aur.70198.
4. Lai MC, Lombardo MV, Suckling J, Ruigrok AN, Chakrabarti B, Ecker C, Deoni SC, Craig MC, Murphy DG, Bullmore ET; MRC AIMS Consortium; Baron-Cohen S. Biological sex affects the neurobiology of autism. Brain. 2013 Sep;136(Pt 9):2799-815. doi: 10.1093/brain/awt216. Epub 2013 Aug 8. PMID: 23935125; PMCID: PMC3754459.
5. Muiño Tato, A.; Marquès-Donoso, A.; Sánchez-Huete, J.C. Gender Bias in ASD Diagnostic and Screening Tools: A Systematic Review and Meta-Analysis. Psychiatry Int. 2026, 7, 145. https://doi.org/10.3390/psychiatryint7040145
6. Cruz S, Zubizarreta SC, Costa AD, Araújo R, Martinho J, Tubío-Fungueiriño M, Sampaio A, Cruz R, Carracedo A, Fernández-Prieto M. Is There a Bias Towards Males in the Diagnosis of Autism? A Systematic Review and Meta-Analysis. Neuropsychol Rev. 2025 Mar;35(1):153-176
7. Steward R, Crane L, Mairi Roy E, Remington A, Pellicano E. "Life is Much More Difficult to Manage During Periods": Autistic Experiences of Menstruation. J Autism Dev Disord. 2018 Dec;48(12):4287-4292. doi: 10.1007/s10803-018-3664-0. PMID: 29982893; PMCID: PMC6223765.
8. Lever AG, Geurts HM. Psychiatric Co-occurring Symptoms and Disorders in Young, Middle-Aged, and Older Adults with Autism Spectrum Disorder. J Autism Dev Disord. 2016 Jun;46(6):1916-1930. doi: 10.1007/s10803-016-2722-8. PMID: 26861713; PMCID: PMC4860203.
9. Baeza-Velasco C, Vergne J, Poli M, Kalisch L, Calati R. Autism in the context of joint hypermobility, hypermobility spectrum disorders, and Ehlers-Danlos syndromes: A systematic review and prevalence meta-analyses. Autism. 2025