Bans on transgender women in international swimming and rugby this week opened the door for track and field to consider following suit in what could turn into a wave of policy changes in Olympic sports.
The announcement Sunday by swimming's governing body, FINA, was followed quickly by a show of support from World Athletics President Sebastian Coe, who was in Hungary for the swimming world championships. He said FINA's decision was in the best interest of swimming and that his own federation, which oversees track and field and other running sports, would review its policies on transgender athletes and intersex athletes at the end of the year.
"If we ever get pushed into a corner to that point where we're making a judgment about fairness or inclusion, I will always fall down on the side of fairness," Coe said.
Experts viewed that as a signal that World Athletics officials could use the FINA precedent to block all transgender and intersex athletes — the latter referred to by clinical terminology as having differences in sex development — from competing in women's events.
FINA's new policy bans all transgender women from elite competitions if they didn't begin medical treatment to suppress testosterone production before either the onset of puberty or by age 12, whichever comes later. USA Swimming put its own policy in place earlier this year, with the idea that it would eventually follow FINA's lead, but this week said it would need time to see how FINA's policy affects its own.
Should track and field adopt a similar rule to FINA, Caster Semenya, an athlete with differences in sex development, still would be kept out of races at her chosen distance, 800 meters.
It also could bar 200-meter silver medalist Christine Mboma of Namibia, who also is an athlete with differences in sex development and expected to contend for the title at world championships in Oregon next month. Currently, World Athletics rules governing such athletes don't apply to the 200-meter race.
"By later this year, I think (World Athletics) will have announced a policy that is very similar to swimming," said Ross Tucker, a science and research consultant for World Rugby. "And they will say that if ever a person has gone through male puberty and has obtained the advantages associated with testosterone, they can't compete in women's sports."
The International Rugby League also barred transgender women from women's matches until more studies allow for the sport's regulators to come up with a cohesive inclusion policy. And the International Cycling Union last week updated its eligibility rules for transgender athletes; it increased the period during which transgender athletes on women's teams must lower their testosterone level to two years rather than one.
FIFA, which runs soccer, said it is "currently reviewing its gender eligibility regulations in consultation with expert stakeholders."
Individual sports are taking the lead because of the International Olympic Committee framework that was introduced last November and went into effect in March placed all sports in charge of their own rules regarding testosterone. It replaced an IOC policy that had allowed transgender women who had been on hormone replacement therapy for at least 12 months to compete in the Olympics against other women.
The new guidance, which is not binding, recommends that testosterone levels should not determine whether someone is eligible to compete — a stance that World Athletics has not adopted.
Tucker said he expected maybe the "big four or five" international sports federations to follow FINA's suit, but not all the others — in part because many are smaller operations that don't have science and legal teams to do the research for thorough policies. FINA had assigned three groups, athletes, science and medicine and legal and human rights, to work on its policy.
FINA's decisions and those of other organizations are likely to be challenged either in court or at the Court of Arbitration for Sport, meaning federations that adopt a rule will need scientific studies and legal funding to back up the policy.
"What swimming did was not easy, and it certainly wasn't cheap," Tucker said.
Coe said FINA "spent $1,000,000 (on legal fees). We're not FIFA but we're not bereft. But there are other sports that are genuinely fearful that, if they go down that road, they'll bankrupt themselves defending this."
Athletes at the world swimming championships in Hungary mostly steered clear of commenting on the new transgender policy this week.
"I think the question is, if you're a woman out there and you're racing someone else, like, how would you feel doing that? It's just about fairness in sport," said Australia's Moesha Johnson, who finished fourth in the 1500 meters.
The FINA decision also sent national swim federations scrambling.
Swimming Australia said it endorses fair and equitable competition for all athletes, adding in a statement: "We also firmly believe in inclusivity and the opportunity for all athletes to experience the sport of swimming in a manner that is consistent with their gender identity and expression."
In the U.S., the NCAA, which governs college sports, had sought clarity from USA Swimming because of transgender swimmer Lia Thomas, who competed on Penn's women's team.
USA Swimming created a policy requiring evidence that an athlete had maintained a testosterone level less than 5 nanomoles per liter for a minimum period of 36 months. But the NCAA decided against immediately adopting that rule, which would have made Thomas ineligible for the national championships in March, where she won the 500-yard individual title.
When it released its policy, USA Swimming said it would remain in place until FINA adopted its own policy. In a statement Wednesday, USA Swimming said it would "now take our time to understand the impact of this international standard on our existing policy."
Thomas has said she would like to pursue the Olympics; if she does, her times would likely put her in the mix to at least earn a spot at Olympic trials for the 2024 Games in Paris.
The Thomas case might ultimately be viewed as the tipping point in international competition, given the relative lack of transgender athletes in elite sports, Tucker said.
"People aren't really very good at understanding an issue until it's right in front of them as a physical thing," Tucker said, "They almost have to be punched in the nose before they think something is real. And Lia Thomas made this real."
AP Sports Writers Ciaran Fahey and Graham Dunbar contributed.