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.

Athletes competing in women’s sports will be asked to undergo one-time genetic testing.

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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 L.A. 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.

Finn Gardiner with the Massachusetts Transgender Political Coalition said she was “dismayed” by the decision.

“The IOC decided to bow to the rising backlash against trans rights, and decided to make a decision based on prejudice rather than actual research about trans athletes and sports,” Gardiner said.

He and other local advocates are frustrated by the ripple effects the decision could have on transgender people.

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“First, you’re gonna have trans people being stigmatized even more because they’re not allowed to play,” Gardiner said. “Also it’s not just trans people that are being barred from competing in the Olympics. It’s also intersex women.”

With the genetic testing component, advocates like Tanya Neslusan, the executive director of MassEquality, point out that some of the people who are excluded may not even know they are intersex.

“They have spent their entire lives training to be in the Olympic Games, only to find out through a reductive test that they have a chromosomal abnormality,” Neslusan said.

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

“We know that this topic is sensitive,” IOC President Kirsty Coventry said in an online news conference to explain the policy.

Coventry and the IOC 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.”

Neslusan said the consequences are likely to spread far beyond the elite Olympic level.

“It’s going to discourage young [transgender] people from participating in sport,” she said. “It’s going to cause enhanced scrutiny and ‘transvestigating’ of athletes at all levels, which is extremely harmful.”

Coventry 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.

“This was a priority for me way before President Trump came into his second term,” Coventry said. “There’s not been any pressure (on) us to deliver anything from anybody outside of the Olympic Movement.”

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 testosterone levels higher than the typical female range, 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.

Performance advantage from testosterone

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 research included “in-depth individual interviews with impacted athletes from around the world.”

The expert group agreed the current gene test is “the most accurate and least intrusive method currently available.” The saliva, cheek swab or blood sample screens 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.

Gardiner pointed to a recent study that finds no physical advantages for trans women athletes over cisgender women.

Athlete appeal to CAS?

The IOC policy can — and likely will — be challenged at the Court of Arbitration for Sport in the Olympic body’s Swiss home city Lausanne, perhaps by an athlete acting alone.

Track athletes Dutee Chand of India and Semenya challenged previous versions of their sport’s eligibility rules at the court.

Any potential appeal would examine science underpinning IOC research which was not published Thursday. A case could occupy much of the near-28 months until the L.A. Olympics open.

“As we know in today’s world,” Coventry said, “any and all rules and regulations at any point in time could always be challenged.”

Women’s boxing champions

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.

The other Olympic boxing champion, Imane Khelif of Algeria, told CNN last month she would take a gene test to be eligible for the L.A. Olympics. She is reportedly preparing for a professional bout next month in Paris.

The IOC document published on Thursday said the male performance advantage over biological women was “10-12% in most running and swimming events,” at least 20% in “most throwing and jumping events” but “can be greater than 100%” for explosive power events including “punching sports.”

Gardiner cited Khelif as an example of cisgender athletes who could be impacted by the ban.

“It’s non-trans, non-intersex people that are going to be affected if they don’t seem traditionally feminine enough,” he said. “They’re going to be accused of being trans or intersex.”

Trump’s executive order

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.