New regulations on testosterone levels were due to come into force on November 1 but will now be delayed until March 26.

It comes with Semenya and Athletics South Africa (ASA) challenging the legality of the rules regarding athletes "with differences of sex development".

Both parties are taking their case to the Court of Arbitration for Sport (CAS) and made an application to delay the rules coming into effect.

The IAAF said they have declined to challenge this as it would cause "additional delay and create new uncertainty for athletes seeking to compete in the women's category".

In return, Semenya and the ASA have agreed to an expedited timetable with CAS hearings due in February prior to a final decision close to the March 26 deadline.

However, in the event of the rules being upheld, the later date means impacted athletes might not be able to compete in time for key outdoor competitions leading up to the World Championships in Doha in September and October.

This is because the IAAF wants to implement a six-month "suppression" period for anyone affected.

IAAF officials remain confident that CAS will eventually rule in their favour, claiming "legal, scientific, and ethical" bases for their rules which have caused widespread debate.

Under the new regulations, athletes competing in events between the 400 metres and the mile, who have testosterone levels of five nmol/L or above and who are androgen-sensitive, must either restrict their levels to five nmol/L through medication or look to compete against men.

It could see Semenya, the double Olympic and triple world champion over 800m, banned unless she agrees to take "corrective" medication. 

The IAAF insist the ruling is not directed at Semenya specifically but she is the only high profile athlete it is set to impact.

They have claimed that female athletes with high testosterone levels have an "enormous advantage" that is comparable to adults competing against children.

Semenya has claimed that "it is not fair that I am told I must change".

She filmed an advert for sports giant Nike which asked questions such as "would it be easier for you if I wasn't so fast?"

Critics of the IAAF have included human rights experts and the Women's Sports Foundation. 

"Prolonging the uncertainty for athletes looking to compete in these distances next year and beyond is unfair and so we have reached a compromise with the claimants," said IAAF President Sebastian Coe. 

"We have agreed not to enforce the regulations against any athlete until the contested regulations are upheld. 

"In exchange, they have agreed not to prolong the process. 

"All athletes need this situation resolved as soon as possible."

In a notification sent to all IAAF Member Federations today, health and science department director Stéphane Bermon said the November date had originally been set to allow athletes to compete in the new season even after the suppression period.

Athletes are now being given the option to start the six months earlier and before the CAS ruling.

Events affected athletes could potentially miss include the Diamond League season which starts in May.

"Although the regulations are formally stayed pending the outcome of the CAS proceeding, the IAAF Health and Science Department stands ready to support athletes and receive biological results from individual athletes wishing to start their six-month suppression period at any time from today," said Bermon. 

ASA said they welcomed the decision to postpone the rules in a statement sent to insidethegames.

"ASA is very pleased with the outcome and accordingly thank the legal teams of ASA and that of athlete Caster Semenya for the hard work done to date," they said.

"The ASA appeal of the regulations is based on a number of points including its discriminatory effect on female athletes like Semenya. 

"The South African legal team will also argue that the medical data relied upon by the IAAF is flawed."