Caster Semenya, an 18-year-old South African, last night won gold in the 800 metres but she may be forced to return the medal if she fails a gender-verification test.

Semenya, unknown on the world stage until this week, is now a world champion but is probably already more notorious for the unfortunate situation where her gender has been officially questioned and where it is publicly known that she has been asked to undergo medical examination to prove that she is female.

Her victory last night was notably dominant, particularly for a newcomer, and comments afterwards from her beaten rivals emphasised the unpleasant situation in which she now finds herself. Mariya Savinova, the Russian who was fifth, raised doubts over the winner’s gender and Elisa Piccione, the Italian who finished sixth, was more damning. “For me, she is not a woman,” Piccione said. No one should be accusing Semenya of cheating, though. Instead, her strength and appearance have raised fears that she may have been born with a rare abnormality, where she has grown up with the genitalia of a woman but the chromosomes of a male.

The storm growing around her is such that last night’s race was a comparative moment’s calm. After she had beaten Kenya’s Janeth Jepkosgei and Britain’s Jenny Meadows into second and third respectively, she did half a lap of honour before being whisked out of the stadium, avoiding the media mixed zone and the winner’s press conference.

In her stead, Pierre Weiss, the IAAF general secretary, answered questions and explained that Semenya has been examined in a Berlin hospital since her arrival here and that if she were found not to be female, the race medals would be redistributed.

The IAAF are having to chase the situation because it was only on July 31, when Semenya won at the African Junior Championships in Bambous, Mauritius, that they first heard of her.

Semenya, from Ga-Masehlong, a village near the northern city of Polokwane, was a first-year sports science student at Pretoria University when she improved her personal best by four seconds in Bambous, delivering the fastest time in the world this year by anyone, junior or senior.

The closer Berlin got, the louder became a whispering campaign against her. Her arrival here was preceded by speculation in athletics chat rooms about her gender. And when she arrived, it only got worse. Down at the warm-up track, she has had rivals pointing, starring and gossiping.

Of course, what Semenya is in need of is not bullying but support. The minute that the IAAF offices in Monaco were notified of her Bambous performance, alarm bells started ringing. The first, clear consideration was whether this might be a case of excessive steroid abuse, but that was easily tested. It was not. When the rumours started, the IAAF contacted the South African federation and requested that the gender-verification process be started. There have now been tests both in South Africa and Berlin.

Gender verification used to be mandatory across Olympic sports but the issue was so delicate and scientifically complicated that it was dropped before the Sydney Olympics. Sports authorities still have to be aware of athletes with what is referred to as “intersex” conditions. That is why, under its Rule 113, the IAAF’s law book says that, “the medical delegate shall have the authority to arrange for the determination of the gender of an athlete should he judge that to be desirable”.

What the IAAF had hoped was that the South Africans would withdraw Semenya from Berlin, to protect her. “We would not have entered her in the female event if we had any doubt,” said a team statement. They have also insisted that they know nothing of the process of gender verification that the IAAF insists has already begun.

Nick Davies, the IAAF spokesman, explained yesterday that “the extremely difficult, complex” gender-verification process involved “an endocrinologist, a gynaecologist, an internal medicine expert, an expert on gender and a psychologist” and would take a matter of weeks.

There are between 20 and 30 different types of “intersex” conditions, each of them affecting the body in different ways, and it is for the medics to decide whether, if Semenya is found to have one of them, the resulting hormonal balance gives her an unfair advantage.

“It will have to be carefully considered,” Davies said. “It is not straightforward.” This is not the first time the IAAF has asked for gender verification though, generally, the athletes have managed to retain their privacy. It remains to be seen whether Semenya appears for today’s medal ceremony. The last athlete to fail a gender test was Santhi Soundarajan, the Indian 800 metres runner, who was stripped of the silver medal she won at the 2006 Asian Games. A year later, she failed in an apparent suicide attempt.

A question of gender

•1966: First gender tests introduced at the European Athletics Championships, where female competitors had to parade unrobed before a panel of physicians. All 243 athletes passed, although only after six athletes from an unnamed Eastern bloc country had withdrawn.

•1968 Olympics: New test introduced by examining cells from a smear taken from the cheek. This soon proved unreliable as a number of female competitors were wrongly disqualified.

•1990: Working body of the IAAF recommends abandoning gender verification tests.

•2000: Before the Sydney Olympics, the IOC decides to abandon all mandatory testing.

•2004: Before the Athens Games, the IOC declares that athletes who have undergone sex changes would be permitted to compete in future Olympics if they have met criteria regarding hormonal treatment and timing of their surgery. Mianna Bagger, the Australian, soon afterwards becomes the first transsexual to compete on the Ladies European Tour.