In a letter sent to the WMA, the IAAF said it "strongly disagrees" with the group's concerns about the validity of the regulations, which came into effect today following last week's Court of Arbitration for Sport (CAS) ruling in its case against Caster Semenya.

The rules mean Semenya, a two-time Olympic and triple world champion over 800 metres, and other affected athletes will have to take medication to reduce their testosterone if they want to continue running on the world stage at events between 400m and a mile.

DSD athletes with naturally high levels of testosterone who wish to participate in events between the two distances must medically limit that level to under 5 nmol/L, double the normal female range of below 2 nmol/L.

In its verdict, which followed months of deliberation in a highly contentious case, the CAS admitted the rules were "discriminatory" but also said the policy was "necessary, reasonable and proportionate" to protect the fairness of women's sport.

The WMA called for the "immediate withdrawal" of the regulations after claiming they were based on "weak evidence from a single study, which is being widely debated by the scientific community".

The body, which claims to represent physicians from 114 member countries, had previously expressed its opposition to medically prescribing treatment to lower testosterone if the condition was not recognised as pathological.

In the letter, the IAAF claimed the rules had been formulated based on "many scientific publications and observations from the field during the past 15 years".

The IAAF wrote that, in 46XY DSD individuals such as Semenya, reducing serum testosterone to female levels by using a contraceptive pill, or other means, is the "recognised standard of care for 46XY DSD athletes with a female gender identity".

"These medications are gender-affirming," the worldwide governing body added in its letter.

The IAAF also stressed how it was up to the athlete to decide whether or not to undergo treatment, such as taking medication or even having surgery.

The regulations effectively ban athletes such as Semenya from competing in races from 400m to a mile if they choose not to take the drugs.

Athletes who want to compete at the 2019 IAAF World Championships, due to take place in Qatar's capital Doha from September 27 to October 6, will have to start taking medication immediately.

Those affected by the rules must undergo a blood sampling by that date to measure their serum testosterone level and test their eligibility. 

Semenya, who has remained defiant despite the verdict, won the women's 800m race in a meeting record time at last week's Diamond League event in Doha.

In a question-and-answer document posted on its website, the IAAF dismissed claims the rules had been targeted at the South African.

"Some commentators have suggested that the regulations were (and have always been) directed at an individual athlete," the organisation said.

"That is not true. 

"The IAAF is bound by strict confidentiality and so simply cannot – and will not – disclose the number of other athletes affected, or the identities of those athletes."