Swimming's world governing body FINA has voted to restrict transgender athletes' participation in women’s elite competitions.
The new policy means transgender athletes will have to have completed their transition by 12 in order to compete in women's elite races.
The decision was made during FINA's extraordinary general congress meeting, and they have revealed plans to establish an "open" category.
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The policy was passed with a roughly 71% majority after it was put to the 152 members of the national federations with voting rights, who attended the congress at the Puskas Arena in Budapest.
The new policy will require transgender swimmers to have completed their transition by the age of 12 in order to be able to compete in events, and opens up eligibility to those who have "complete androgen insensitivity and therefore could not experience male puberty".
The decision has been described as "only a first step towards full inclusion" for transgender athletes.
FINA president Husain Al-Musallam said: "We have to protect the rights of our athletes to compete, but we also have to protect competitive fairness at our events, especially the women's category at FINA competitions.
"FINA will always welcome every athlete.
“The creation of an open category will mean that everybody has the opportunity to compete at an elite level. This has not been done before, so FINA will need to lead the way. I want all athletes to feel included in being able to develop ideas during this process."
FINA members heard a report from a transgender task force made up of leading figures from the world of medicine, law and sport.
Executive director of the governing body Brent Nowicki said: "FINA's approach in drafting this policy was comprehensive, science-based and inclusive, and, importantly, FINA's approach emphasised competitive fairness.”
Transgender rights in sport have been under the spotlight recently, after University of Pennsylvania swimmer Lia Thomas became the first transgender NCAA champion in Division I history after winning the women's 500-yard freestyle earlier this year.
History was also made at the Tokyo 2020 Olympic Games when New Zealand’s Laurel Hubbard competed in the women’s weightlifting event.
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