London

World Athletics chief Sebastian Coe says women's sport faces a "fragile" future unless sporting federations get the regulations right over the participation of transgender athletes.

His warning comes after American swimmer Lia Thomas became the first transgender athlete to win a National Collegiate Athletic Association (NCAA) top tier title with victory in the 500-yard (457 metres) freestyle.

Thomas has dominated US collegiate women's swimming recently as a student athlete at the University of Pennsylvania, where she previously competed as a man.

Her case has divided opinion, with some -- including several teammates -- arguing she has an unfair physiological advantage and should be barred from competing, while others say she should be allowed to compete freely as a woman.

Coe, the president of track and field's governing body, acknowledged the issue was fraught but said it was vital to get the regulations right.

"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 told the Times.

"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."

Former British Olympic middle-distance gold medallist Coe said "gender cannot trump biology" when it comes to deciding whether trans athletes should be allowed to compete in women's events.

Under World Athletics rules, trans women have to show they have low testosterone levels for at least 12 months before competition.

Coe highlighted the "residual impact" of transitioning, adding: "There is no question that testosterone is the key determinant in performance."

He said: "It's really difficult to keep the emotion out of this and subjectivity, so we do have to really stick as closely as we can to the science -- and that's what we've always tried to do when it's been uncomfortable."