World Athletics president Sebastian Coe says the "integrity of women's sport" is under threat after Lia Thomas became the first transgender woman to win a US National Collegiate Athletic Association (NCAA) swimming event. 

Thomas made history last week by winning the women's 500-yard freestyle in Atlanta.

"I think that the integrity of women's sport — if we don't get this right — and, actually, the future of women's sport, is very fragile," Coe said on Monday.

"These are sensitive issues, they are societal issues — they go way, way beyond sport. I don't have the luxury to get into endless discussions or the school of moral philosophy."

Thomas competed on the men's team for three years before transitioning and moving to the women's team and setting multiple program records.

Last month, USA Swimming unveiled a new policy to allow transgender athletes to swim in elite events by setting out criteria that aim to mitigate any so-called unfair advantages.

The rules include testing to ensure testosterone is below a certain level — five nanomoles per litre continuously for at least 36 months — in transgender athletes who wish to compete against cisgender female swimmers.

World Athletics requires transgender athletes to have low testosterone levels for at least 12 months before competition, a time period Coe thinks is too short.

"We are asking for a greater length of [time] before competition because the residual impact of transitioning like that is more profound," he said.

"There is no question that testosterone is the key determinant in performance."

Transgender rights have long been a controversial and politically divisive issue in the United States, from sport to serving in the military and what bathrooms people are allowed to use.

However, trans advocates have regularly pushed back against arguments that exclude trans people from the right to participate in sport, and have challenged claims that trans women have dominated women's sport.

These issues recently came to a head in an Australian context with Liberal senator Claire Chandler's attempt to introduce a private member's bill to the Senate to amend laws relating to sex discrimination in sport — a move supported by Prime Minister Scott Morrison, who called it a "terrific bill". 

At the time, former Tasmanian anti-discrimination commissioner Robin Banks called the bill "a legislative solution to a non-existent problem".

"This is not a good piece of legislation, it will have unintended consequences and discrimination laws should be about preventing discrimination, not promoting it," she said.

Reuters/ABC