Monaco - The governing body of track and field will not apply rules to limit natural testosterone levels in female runners until the Court of Arbitration for Sport concludes an appeal case brought by South Africa's Olympic champion Caster Semenya.
The IAAF said on Tuesday it agreed to postpone the intended November 1 start for eligibility rules until CAS gives a verdict "expected on or before" March 26.
That target date is six months and two days before the start of the 2019 world championships in Doha, Qatar.
If the IAAF's rules for athletes with differences of sex development (DSD) are upheld by the court, female runners will be forced to medicate to reduce their testosterone levels for six months before racing internationally from 400m through the mile.
Semenya is the current 800m world champion and a likely favourite for a fourth world title to add to her two Olympic gold medals. She also took bronze in the 1 500m at the 2017 worlds in London.
The IAAF expects a February appeal hearing for Semenya, who could have sought an interim ruling from CAS to freeze the rules if the track body pressed ahead with its planned start date.
"The IAAF remains very confident of the legal, scientific, and ethical bases for the regulations, and therefore fully expects the Court of Arbitration for Sport to reject these challenges," the Monaco-based organisation said.
The revised timetable could wreck the outdoor track season for Semenya and other runners with high natural testosterone levels who do not opt to begin medicating before the verdict.
If Semenya's appeal is dismissed, she would be ineligible for the entire circuit of top-tier Diamond League meetings, which run from May to September.
The IAAF said it was ready to "receive biological results from individual athletes with DSDs."
"Athletes wishing to begin their six-month period sooner than the end of March should contact me directly," health and science director Stephane Bermon said in an IAAF statement.