How common is intersex?
To answer this question in an uncontroversial way, you’d have to first get everyone to agree on what counts as intersex —and also to agree on what should count as strictly male or strictly female. That’s hard to do. How small does a penis have to be before it counts as intersex? Do you count “sex chromosome” anomalies as intersex if there’s no apparent external sexual ambiguity?[1] (Alice Dreger explores this question in greater depth in her book Hermaphrodites and the Medical Invention of Sex.)
Here’s what we do know: If you ask experts at medical centers how often a child is born so noticeably atypical in terms of genitalia that a specialist in sex differentiation is called in, the number comes out to about 1 in 1500 to 1 in 2000 births. But a lot more people than that are born with subtler forms of sex anatomy variations, some of which won’t show up until later in life.
Below we provide a summary of statistics drawn from an article by Brown University researcher Anne Fausto-Sterling.2 The basis for that article was an extensive review of the medical literature from 1955 to 1998 aimed at producing numeric estimates for the frequency of sex variations. Note that the frequency of some of these conditions, such as congenital adrenal hyperplasia, differs for different populations. These statistics are approximations.
Not XX and not XY one in 1,666 births
Klinefelter (XXY) one in 1,000 births
Androgen insensitivity syndrome one in 13,000 births
Partial androgen insensitivity syndrome one in 130,000 births
Classical congenital adrenal hyperplasia one in 13,000 births
Late onset adrenal hyperplasia one in 66 individuals
Vaginal agenesis one in 6,000 births
Ovotestes one in 83,000 births
Idiopathic (no discernable medical cause) one in 110,000 births
Iatrogenic (caused by medical treatment, for instance progestin administered to pregnant mother) no estimate
5 alpha reductase deficiency no estimate
Mixed gonadal dysgenesis no estimate
Complete gonadal dysgenesis one in 150,000 births
Hypospadias (urethral opening in perineum or along penile shaft) one in 2,000 births
Hypospadias (urethral opening between corona and tip of glans penis) one in 770 births
Total number of people whose bodies differ from standard male or female one in 100 births
Total number of people receiving surgery to “normalize” genital appearance one or two in 1,000 births
1 Dreger, Alice Domurat. 1998. Ambiguous Sex—or Ambivalent Medicine? Ethical Issues in the Treatment of Intersexuality. Hastings Center Report, 28, 3: 24-35.
2 Blackless, Melanie, Anthony Charuvastra, Amanda Derryck, Anne Fausto-Sterling, Karl Lauzanne, and Ellen Lee. 2000. How sexually dimorphic are we? Review and synthesis. __American Journal of Human Biology__ 12:151-166.
We were recently asked to update these frequency figures, and a lively discussion arose between two staff members.
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