The International Olympic Committee is moving towards a blanket ban on transgender women from women's sport, Sky News understands.
Olympic chiefs are also looking at prohibiting athletes with DSD (differences of sex development) from women's events given testosterone advantages.
It follows a presentation last week to IOC members by their medical chief, Dr Jane Thornton, which highlighted the potential physical advantages of competing in women's sport after being born male.
IOC members were also updated on how sex testing would work - as World Athletics has already introduced to verify biological sex to compete in women's events.
A ban on transgender women from women's events could be introduced in time for the 2028 Los Angeles Olympics, although the issue has not been presented to the full IOC Session for a decision yet.
It follows pressure from US President Donald Trump, vowing to end the "war on women's sports".
He said in February: "In Los Angeles in 2028, my administration will not stand by and watch men beat and batter female athletes.
"We're not going to let it happen.
"Just to make sure, I'm also directing our secretary of homeland security to deny any and all visa applications made by men attempting to fraudulently enter the US while identifying as women athletes to try and get into the games."
The IOC convened experts in September on a working group to reassess rules on gender eligibility in the Olympics after leaving it for each sport to decide themselves.
The IOC confirmed to Sky News: "An update was given by the IOC medical and scientific director to the IOC members last week at the commission meetings.
"The working group is continuing its discussions on this topic and no decisions have been taken yet.
"Further information will be provided in due course."
The IOC introduced "certificates of femininity" at the 1968 Mexico Games.
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But those chromosome-based tests were deemed unscientific and unethical and were dropped ahead of Sydney 2000.
But World Athletics this year introduced what it calls non-invasive cheek swab tests to detect the presence of the male Y chromosome.
The IOC has previously called a return to sex testing a "bad idea", but new president Kirsty Coventry has talked about protecting the female category since her election in March.
(c) Sky News 2025: Olympics organisers moving towards blanket ban on transgender women from women's sport
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