On the number of intersex people

This article reviews available data on the number of intersex people. It does not review legal sex assignments, gender identities or sexual orientations, and nor does it (or should it) define intersex in such ways. For information on the diverse ways in which people born with intersex traits understand our bodies, sexes and genders, these matters are introduced in the following articles:

In summary, there are no firm population figures for people with intersex variations. The reasons for this lie in the lack of accurate recording of data on intersex diagnoses, but factors are also arbitrary and suffer from ideological values.

We have seen estimates range from 1 in 1,500 or 2,000 births to 4%, and we recommend a figure of 1.7%, despite its flaws. This was published by Blackless and others in the American Journal of Human Biology, and also by Anne Fausto-Sterling, Professor of Biology and Gender Studies at Brown University in the US. No more accurate sources of data yet exist.

Upper bound estimates

The higher figure of 4% was apparently first quoted by John Money, PhD. Money was regarded as a preeminent authority on intersex issues until the late 1990s and revelations regarding the David Reimer case; this classic medical case study concerned the gender identity of a boy raised as a girl after a botched circumcision.

Professor Anne Fausto-Sterling quoted Money’s estimate in her paper, The Five Sexes. This figure was then cited by Cheryl Chase of the (now defunct) Intersex Society of North America in her 1993 letter Intersexual Rights to The Sciences journal.

Mid-range estimate

In the absence of better internationally-accepted data, Intersex Human Rights Australia cites a systematic review of medical literature in the American Journal of Human Biology by Melanie Blackless, Anne Fausto-Sterling and others showing intersex to be around 1.7% of all live births.

This estimate relates to any “individual who deviates from the Platonic ideal of physical dimorphism at the chromosomal, genital, gonadal, or hormonal levels” and thus it encapsulates the entire population of people who are stigmatised – or risk stigmatisation – due to innate sex characteristics.

Lower bound estimates

Many sources cite lower bound estimates of 1 in 1,500 or 1 in 2,000 live births. These tend to exclude many intersex variations that are otherwise considered by medicine now to be “Disorders of Sex Development” or “DSD”; they focus on a narrower range of traits where external genitalia are “ambiguous” and diagnosis is made at birth. For example, Professor Alice Dreger has said, in 1998:

One 1993 gynecology text estimates that “in approximately 1 in 500 births, the sex is doubtful because of the external genitalia.” I am persuaded by more recent, well-documented literature that estimates the number to be roughly 1 in 1,500 live births.

The frequency estimate goes up dramatically, however, if we include all children born with what some physicians consider cosmetically “unacceptable” genitalia.

Because of its focus on characteristics visible immediately at birth, it excludes traits that may be evident through prenatal screening or genetic testing of IVF embryos, and it excludes traits that become evident at puberty or later in life.

A distinct narrow approach is also seen in a 2002 paper by Dr Leonard Sax which states:

Anne Fausto-Sterling’s suggestion that the prevalence of intersex might be as high as 1.7% has attracted wide attention in both the scholarly press and the popular media. Many reviewers are not aware that this figure includes conditions which most clinicians do not recognize as intersex, such as Klinefelter syndrome [47,XXY], Turner syndrome [45,X], and late-onset adrenal hyperplasia. If the term intersex is to retain any meaning, the term should be restricted to those conditions in which chromosomal sex is inconsistent with phenotypic sex, or in which the phenotype is not classifiable as either male or female. Applying this more precise definition, the true prevalence of intersex is seen to be about 0.018%, almost 100 times lower than Fausto-Sterling’s estimate of 1.7%.

This statement actually contains two distinct definitions (separated by the word “or”) relating to phenotypes and chromosomes. It is an arbitrary and ideological analysis that requires individuals who have come to the attention of medicine due to their innate physical characteristics to be investigated as to the cause.

Our recommendation: use the mid-range estimate, for now

IHRA does not agree with the analysis by Sax, largely because we attribute a different meaning to the word intersex, based on lived experience. Many people who fall outside Sax’s narrow definition nevertheless face stigmatisation and suffer human rights violations because physical development does not conform to medical or social norms for female or male bodies. Many such individuals, including people with XXY, hypospadias and MRKH, have helped found and help lead the intersex human right movement.

In this sense, the difference between narrow and broad definitions in medicine is arbitrary and ideological. It is arbitrary in that investigation and testing is required to establish the cause of relevant biological characteristics. It is ideological in that intersex people share common ground in the stigmatisation of our atypical sex characteristics, and we refute social and cultural grounds for the medicalisation of intersex bodies. It is the perceived need for diagnosis and treatment itself that defines the intersex population, and not necessarily a specific and narrow set of causal factors.

In this context, a 2006 shift in medical terminology is illuminating. “DSD” was defined by clinicians as a “replacement” medical term for hermaphrodite, pseudo-hermaphrodite and intersex. The term itself remains highly contested: Australian and many other intersex organisations regard it as inherently pathologising; it tends to sanction medical intervention. Our contention was supported by the Australian Senate’s Community Affairs Committee in a 2013 report on the Involuntary or coerced sterilisation of intersex people in Australia.

Even though we object to the term “DSD”, it encapsulates a range of atypical physical or anatomical sex characteristics. These share in common their non-conformance with medical and social sex and gender norms. This non-conformance with stereotypical standards for male and female is why intersex differences are medicalised in the first place and, while that remains the case, it makes sense to us to include them in a definition of intersex.

The low figure of 1 in 1,500 or 1 in 2,000 live births is not borne out by data published elsewhere. The NSW Ministry of Health reports data from the State’s Mothers and Babies Report 2009 showing that infants with visible reportable differences of sex anatomy between 2003-2009 comprised 0.59% of all births, or 1 in 169. No breakdown of additional (often not yet apparent) relevant chromosomal “anomalies” is given.

Thus, in the absence of better internationally-accepted data, Intersex Human Rights Australia cites a systematic review by Blackless, Fausto-Sterling and others showing intersex to be around 1.7% of all live births. In Sexing the Body, Anne Fausto-Sterling includes the following summary:

Frequencies of Various Causes of Nondimorphic Sexual Development
Cause Estimated frequency per 100 live births
Non-XX or non-XY (except Turner’s or Klinefelter’s) 0.0639
Turner Syndrome (45,X or 45,XO) 0.0369
Klinefelter Syndrome (47,XXY) 0.0922
Androgen Insensitivity Syndrome (i.e. Complete AIS) 0.0076
Partial Androgen Insensitivity Syndrome (PAIS) 0.00076
Classic CAH (omitting very high frequency population) (Congenital Adrenal Hyperplasia) 0.00779
Late-onset CAH 1.5
Vaginal agenesis 0.0169
True hermaphrodites (now termed ‘Ovotestis’) 0.0012
Idiopathic 0.0009
Total 1.728
Source: Anne Fausto-Sterling, 2000, Sexing the Body, Basic Books, page 53. ISBN 978-0465077144
Our notes on terminology are emphasised in italics.

The background analysis published by Blackless and others found that:

frequency may be as high as 2% of live births. The frequency of individuals receiving “corrective” genital surgery, however, probably runs between 1 and 2 per 1,000 live births (0.1-0.2%).

Caveats

Multiple factors affect the accuracy of these statistics, and rates of pregnancy terminations and genetic diversity in different populations mean that the figure is somewhat flawed.

Genetic differences vary in different populations

Because intersex is innate, typically genetic, population figures vary somewhat around the world, and the figure of 1.7% omits populations with high rates of CAH. Fausto-Sterling states:

The figure of 1.7 percent is an average from a wide variety of populations; the number is not uniform throughout the world…
The frequency of the gene for CAH varies widely around the world. One study found that 3.5 per thousand Yupik Eskimos born had a double dose of the CAH gene. In contrast, only 0.005/1,000 New Zealanders express the trait…
Among Ashkenazic Jews, the number [of a related gene] rises to 37/1,000.

In an Australian context, higher than average population figures for CAH are also apparent in some indigenous communities. 5 Alpha-Reductase Deficiency is noted to be relatively more common amongst some linguistic groups in PNG.

There are many more intersex variations

Not all known intersex traits are included in the table. These include diagnoses like 5 alpha-reductase deficiency and complex hypospadias.

Fausto-Sterling’s figure for idiopathic intersex traits is also important to note. Idiopathic diagnoses are those where the aetiology (cause or history) is not known. In 2013, Professor Olaf Hiort, chief of the Division of Paediatric Endocrinology and Diabetes in the Department of Paediatrics at Lübeck University, Germany, has cited “at least 40” distinct intersex variations, also identifying a large range of individuals without specific identified genetic causes:

DSD comprise a heterogeneous group of differences of sex development with at least 40 different entities of which most are genetically determined. An exact diagnosis is lacking in 10 to 80% of the cases.

Ten to 80% is an extraordinary range. It illustrates that neither diagnosis, nor definition (and, we argue elsewhere, nor treatment) are exact sciences.

Anne-Fausto Sterling also suggests that population figures “may be on the rise”, noting a birth via in vitro fertilisation, and concern regarding “environmental pollutants that mimic estrogens”.

Terminations and IVF

On the other hand, population figures are likely to have changed over time due to terminations and the use of IVF to exclude embryos with intersex variations. For example, CAH, 45,X and 47,XXY are testable via amniocentesis, and many identified pregnancies may be terminated including up to 88% in studies of 47,XXY foetuses diagnosed prenatally. (This raises issues within “LGBTI” populations.)

Recommendation

Given that intersex people only come to the attention of data collectors through chance or an apparent medical reason, the actual numbers of people with intersex variations are likely to be as much as 1.7%. Despite the limitations of the data, 1.7% seems more justifiable than alternatives, to date.

Related information

Key references