Swimming's world governing body Fina has banned transgender swimmers from women's elite events if they have begun male puberty.
The new rules, decided during an extraordinary general congress in Hungary overnight, means transgender competitors need to have completed their transition by the age of 12 in order to be able to compete in women's events.
David Gerrard is a professor in sports medicine, a former Olympic swimmer for New Zealand and the vice chair of Fina's sports medicine committee.
He spoke to Susie Ferguson.
