Extensive physical examinations of Semenya, who is just 18 and from a remote village in the country's far north, has shown the athlete is technically a hermaphrodite. Medical reports indicate she has no ovaries, but rather has internal male testes, which are producing large amounts of testosterone.
The presence of both male and female characteristics will come as a devastating blow to Semenya, who has fought off snide remarks about her masculine appearance for much of her life.
Late last night the IAAF was trying to contact the athlete to inform her of the results. After her domination of the world titles in Berlin last month, Semenya was given exhaustive blood and chromosome tests as well as a gynaecological examination.
It is believed the IAAF was hoping to consider the ramifications of the results before publishing details.
One possibility would be to allow Semenya to retain her gold medal, but award a second gold to the runner-up, Janeth Jepkosgei from Kenya.
"This is a medical issue and not a doping issue where she was deliberately cheating," an IAAF spokesman, Nick Davies, told the Herald.
"These tests do not suggest any suspicion of deliberate misconduct but seek to assess the possibility of a potential medical condition which would give Semenya an unfair advantage over her competitors. There is no automatic disqualification of results in a case like this."
Earlier the IAAF said it was likely that Semenya would keep her medal because the case was not related to a drug matter.
Following her stunning victory, Semenya was embroiled in controversy, but returned to South Africa as a hero. South Africans condemned the scrutiny of Semenya and an African National Congress politician has filed an official complaint with the United Nations High Commissioner for Human Rights.
The president of Athletics South Africa, Leonard Chuene, said he was unaware the tests had been completed.
