By Emma Wilkinson
BBC News health reporter
Reports suggest that gender tests on 800m world champion Caster Semenya have shown both male and female characteristics.
The results are still to be examined by a team of experts and it is likely to be a few weeks before the IAAF confirms the reports or announces further detail.
The delay highlights the complexity involved in diagnosing intersex conditions, an umbrella term for a wide range of developmental differences in the reproductive and sexual systems in the body.
How do you define sex?
Peter Bowen-Simpkins, spokesperson for the Royal College of Obstetricians and Gynaecologists and an expert in these conditions, explains there are four types of sex.
There is your phenotype, which is what you look like, your psychological sex, which is what you feel like and which usually the same as your phenotype and related to how you have been brought up.
There is also your gonadal sex which is whether you have ovaries or testicles and your chromosomal sex which is what combination of x or y chromosomes you have.
It is the chromosomes that direct, through the production of hormones, the development of a baby in the womb down a male or female route.
A diagnosis of an intersex condition is not just based on anatomy but is dependent on genetic, hormonal and other factors.
The World Health Organisation points out that gender is a social construct.
When people refer to gender testing, what they are really talking about is biological sex.
A person's view of their gender may be different from the biological sex assigned to them.
How common are intersex conditions?
The prevalence of different intersex conditions is difficult to estimate, partly because it depends on the definition.
But there are dozens of conditions which fall under this category.
And it is thought that around one in 3,000 UK children is born with a noticeable intersex disorder.
Some conditions may only become apparent later in life, if at all.
How do such conditions arise?
In the womb the chromosomes determine whether the foetus develops as a male or female by controlling what hormones are produced.
But errors can occur in this pathway.
For example, in a common condition called androgen insensitivity syndrome, the foetus has male chromosomes but it does not respond to testosterone.
As a result, the baby develops down the "default" female route.
The testes are there but usually do not descend and remain hidden in the body and the condition does not become apparent until adolescence when the girl does not start her period.
"It is all about how you define sex and the fact you have acquired a male chromosome which does not work is not what makes you male," says Mr Bowen-Simpkins.
"These girls are female to look at and feel very female."
In another condition called congenital adrenal hyperplasia, the foetus is female but produces lots of testosterone leading to the development of male genitalia.
What other conditions are there?
Other disorders include having an abnormal number sex chromosomes, including Turner syndrome, where individuals have one x chromosome and no y chromosome.
In Klinefelter's syndrome, males have two or more x chromosomes in addition to one y chromosome which leads to abnormal development of the testis and low levels of testosterone.
Men who inherit an extra y chromosome are usually taller than average and are prone to acne because of high levels of testosterone.
It has also been linked with learning difficulties and behavioural problems.
In some rarer conditions apparent from birth, decisions over what sex to assign the baby can be very difficult.
"I have looked after someone in the past couple of years who was diagnosed as female at birth who then turned out to be male and converted to male in their 30s," says Mr Bowen-Simpkins.
"They went on to produce sperm and father a baby through IVF."
How is the psychological aspect dealt with?
If an intersex condition becomes apparent or is diagnosed in adolescence or adulthood, the impact on the individual whose gender is under question can be profound.
Semenya won gold in the 800m in Berlin in August
It is vital that discussions around intersex conditions are handled sensitively and patients are offered the right support, says Mr Bowen-Simpkins.
In the case of Caster Semenya it must have been a nightmare for her and her family, he adds.
"Psychologically it must be torture.
"They have in good faith brought her up as a girl and now they are being told different.
"It is impossible to say what condition she may have, but in the end it would have to be her decision as to what she felt like.
"She is an adult and the decision on things like whether to have surgery must be hers alone."
He added: "The single most important thing is getting the right support and counselling and I sincerely hope she's getting it."