Semenya celebrates her gold, which came just hours after the IAAF called for a gender test on the athlete.
The 18-year-old won gold in the 800 meters race Wednesday but she may be forced to return the medal if she fails a gender-verification test imposed by the International Association of Athletics Federations (IAAF).
According to media reports, the IAAF are testing to see whether Semenya has a rare genetic disorder that means she has female genitalia but male chromosomes.
This condition, known as intersex, is commonly referred to as hermaphroditism. (Some support groups say that the term "hermaphroditism" can be inaccurate and offensive, as it implies that someone is both fully male and fully female, which is a physiologic impossibility.)
According to the Intersex Society of North America, (ISNA) intersex is a "general term used for a variety of conditions in which a person is born with a reproductive or sexual anatomy that doesn't seem to fit the typical definitions of female or male."
"For example, a person might be born appearing to be female on the outside, but having mostly male-typical anatomy on the inside," a statement on the society's Web site says.
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There are around 20 to 30 types of biological "intersex" conditions, each of them affecting the body in different ways.
Some people are born with both male and female reproductive organs, while others like intersex activist Hida Viloria are born biologically female yet possess masculine-looking genitalia.
Others have a form known as Androgen Insensitivity Syndrome (AIS) where the person is totally insensitive to any male hormones known as androgens.
Dr. Peter Bowen-Simpkins of the UK's Royal College of Obstetricians and Gynaecologists told CNN: "Intersexuality is incredibly rare, the one I've seen most commonly and one which affects 1 in 13,000 people worldwide is AIS."
Women's world champion Semenya faces gender test
"In a woman your androgen receptors leads you to grow pubic hair, for instance," he explained. "If you are insensitive to androgens, you will grow up looking like a girl because the default of all human beings is female.
"However if the body, when it's developing, is not guided into turning into a male, then it will always be female," he told CNN.
He added: "This South African athlete couldn't have AIS because her problem is that it is suggested that she looks rather male, she's got a big jaw and has very little breast development, but so many athletes are like that, " he added.
"But if she had AIS she would be all female and wouldn't have the advantage of the testosterone androgen, which make men's bones grow and makes them faster than a woman."
To test Semenya's gender, Dr. Bowen-Simpkins said the IAAF test would involve her being examined by a gynecologist to see what her genitals look like. Semenya would also have an ultrasound to see if she has all the normal female reproductive organs.
Doctors would also need an hormonal test to see if she had an excess of testosterone and they would also test her chromosomes.
People who are intersex could also have the condition and not be aware of it, as was the case of Indian athlete Santhi Soundarajan, who failed a gender test at the 2006 Asian games and was stripped of her medal. She later attempted suicide, survived and recently announced she was becoming a coach.
Intersex conditions occur in one out of every 2,000 births in the United States, according to the Rohnert Park, California-based Intersex Society of North America.
For more than half a century it was common for doctors to carry out reversal operations, either through castration or constructing a new vagina, on babies whose genitals were seen as either too big or too small.
Many of these people later spoke out and said that these surgeries caused them trauma and confusion in adult life.
Most groups campaigning for intersex people now advocate that doctors should not perform medically unnecessary genital surgeries on intersex babies to make them male or female.
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