The International Olympic Committee's plans for introducing stricter guidelines over transgender athletes before Tokyo 2020 have hit a roadblock because scientists cannot agree.

It was expected they would recommend halving permitted testosterone levels for transgender women in elite sport but due to the sensitive political nature of the subject, draft guidelines have been put on hold.

It now seems unlikely that any decision will be made on the new rules prior to next year's Olympics.

Since the current IOC rulings were introduced in 2015, athletes who have transitioned from male to female are permitted to compete without testes removal provided their testosterone levels remain below 10 nanomoles/litre for a year minimum.

These guidelines are used as a basis for transgender policies among most sports federations but have proved controversial due to the difference in base testosterone levels in men and women. Women's testosterone levels usually range from 0.12 to 1.79 nmol/l, while men's are a much higher level ranging from 7.7 to 29.4 nmol/l.

Some IOC scientists argue that a reasonable compromise would be reducing permitted testosterone levels to 5nmol/l as this is below most males. This would mean that transgender women could still compete in the women's categories but the advantages of male puberty would be taken away.

Others disagree, highlighting the findings from the Karolinska Institute in Sweden, which showed that even after a year of testosterone suppression in transgender women, there is little effect on reducing muscle strength.

High profile athletes such as Martina Navratilova, Sharron Davies, and Daley Thompson have spoken about the impact the inclusion of transgender athletes could have on women's sport.

“To protect women’s sport, those with a male sex advantage should not be able to compete in women’s sport,” said Davies.

While Thompson added: "It's depressing because it has the potential to put an end to women's sport. 

"Theoretically I can identify as a lady and go and compete." 

Many sports are currently unclear on where they stand. Last year Hannah Mouncey, who had previously competed for the Australian men's handball team, was told she couldn't compete in the professional women's Australia rules football league due to her strength and physique.

In the same year, New Zealand weightlifter, Laurel Hubbard, who had previously taken part in the men's competition before transitioning aged 35, was permitted to take part in the 2018 Commonwealth Games and the Asian games, where she won gold in the 90+kg category.