Swimming's world governing body, Fina, has voted to restrict transgender swimmers from competing in women's elite events.
The organisation took its vote on the matter during an extraordinary general congress at the World Championships in Budapest, where 152 Fina members submitted their decision on the matter.
A total of 71 percent of voters opted to stop trans athletes from competing in women's elite races if they have gone through any part of the process of male puberty, meaning transgender competitors will have now had to have completed their transition by the age of 12 - i.e. have had male puberty suppressed by hormone blockers prior to the age of 12 - in order to compete.
Rather than excluding transgender women from swimming altogether, the governing body will aim to establish an 'open' category at competitions for those whose gender identity is different than their sex assigned at birth.
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The vote took place after Fina members heard a report from a transgender task force which included leading figures from the world of medicine, law and sport. For the last few months, the organisation has been working to try and come up with competition standards for transgender athletes.
Including transgender women in swimming became a point of contention for many after Lia Thomas became the first openly transgender woman to win a NCAA Division I women's swimming title earlier this year.
Thomas has expressed plans to continue competing after she finished college, though the new regulations could have a major impact on her ability to do so.
Earlier this year, International Olympic Committee president Thomas Bach said sport cannot have a 'one size fits all' approach to transgender inclusion, arguing that sporting organisations were focused on 'creating a fair competition'.
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"On the grassroots level, sport has to be inclusive, everybody has to have the access to sport," he continued, per Sky Sports. "When it comes to competition as sport, we have to ensure fair competition. That means that you have to find out sport by sport, even discipline by discipline, where there is maybe an unfair advantage."
Karen Pickering MBE, head of swimming at Ardingly College, discussed Fina's decision in a post on Twitter in which she explained she was at the Fina congress for the presentation, discussion and vote on transgender policy.
Pickering commented: "I can vouch for the care and empathy displayed for any athletes who won't now be able to compete in the category their gender ID may align to."
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Some of those in favour of excluding transgender athletes from women's sports have claimed trans competitors have an unfair advantage.
Topics: Swimming