Transgender women athletes are now excluded from women's events at the Olympics after the IOC agreed to a new eligibility policy on Thursday which aligns with U.S. President Donald Trump's executive order on sports ahead of the 2028 Los Angeles Games.

"Eligibility for any female category event at the Olympic Games or any other IOC event, including individual and team sports, is now limited to biological females," the International Olympic Committee said, to be determined by a mandatory gene test once in an athlete's career.

It is unclear how many, if any, transgender women are competing at an Olympic level. No woman who transitioned from being born male competed at the 2024 Paris Summer Games, though weightlifter Laurel Hubbard did at the Tokyo Olympics in 2021 without winning a medal.

The eligibility policy that will apply from the LA Olympics in July 2028 "protects fairness, safety and integrity in the female category," the IOC said.

"It is not retroactive and does not apply to any grassroots or recreational sports programs," said the IOC, whose Olympic Charter states that access to play sport is a human right.

After an executive board meeting, the International Olympic Committee published a 10-page policy document which also restricts female athletes such as two-time Olympic champion runner Caster Semenya with medical conditions known as differences in sex development, or DSD.

The IOC and its president, Kirsty Coventry, have wanted a clear policy instead of continuing to advise sports' governing bodies who previously have drafted their own rules.

"At the Olympic Games, even the smallest margins can be the difference between victory and defeat," Coventry, a two-time Olympic gold medalist in swimming, said in a statement. "So, it is absolutely clear that it would not be fair for biological males to compete in the female category."

She set up a review of "protecting the female category" as one of her first big decisions last June as the first woman to lead the Olympic body in its 132-year history.

Female eligibility was a strong theme in a seven-candidate IOC election last year -- held after a furor around women's boxing in Paris -- when Coventry's main rivals pledged a stronger policy to leading on the issue.

Before the 2024 Paris Olympics, three top-tier sports -- track and field, swimming and cycling -- excluded transgender women who had been through male puberty. Semenya, who was assigned female at birth in South Africa and has high natural testosterone levels, won a European Court of Human Rights judgment in her years-long legal challenge to track and field's rules which did not overturn them.

The IOC document details its research that being born male gives physical advantages that a working group of experts believes are retained.

"Males experience three significant testosterone peaks: In utero, in mini-puberty of infancy and beginning in adolescent puberty through adulthood," the document said.

It added this gives males "individual sex-based performance advantages in sports and events that rely on strength, power and/or endurance."

The IOC said its expert group agreed the current gene test is "the most accurate and least intrusive method currently available." It screened for "the SRY gene, a segment of DNA typically found on the Y chromosome that initiates male sex development in utero and indicates the presence of testes/testicles."

Still, the mandatory gender screening -- already conducted by the governing bodies of track and field, skiing and boxing -- is likely to be criticized by human rights experts and activist groups.

One of the two women's boxing gold medalists at the center of the gender controversy in Paris, Lin Yu-ting of Taiwan, has passed her gene test and can return to competition, the World Boxing governing body said last week.

In the U.S., President Trump signed the executive order "Keeping Men Out of Women's Sports" in February last year, and pledged to deny visas to some athletes attempting to compete at the L.A Olympics. The order also threatened to "rescind all funds" from organizations that allowed transgender athletes to take part in women's sports.

Within months the U.S. Olympic body updated its guidance to national sports bodies citing an obligation to comply with the White House.