(BBC) Trans female athletes must lower their levels of testosterone, athletics' governing body the IAAF has ruled.
Competitors must now keep their levels of natural testosterone below five nanomoles per litre of blood in order to compete in the female category.
The IAAF's previous limit for natural testosterone was 10 nanomoles.
The new regulation is the same as that which applies to athletes with differences of sexual development (DSD), including Caster Semenya.
Semenya is challenging the IAAF's new rules that she and other athletes with DSD must take testosterone-reducing medication in order to compete in track events from 400m to the mile or change to another distance.
The new rules on natural testosterone levels were announced on Monday following a meeting of the IAAF Council in Doha.
Under the new regulations a transgender female athlete is no longer required to be recognised by law in her new gender but should provide a signed declaration that her gender identity is female.
She must demonstrate that the testosterone level in her serum has been less than five nanomoles continuously for a period of at least 12 months prior to being declared eligible, and must keep below that level to maintain eligibility to compete in the female category.