  To police sex segregation in competition, sports authorities have adopted a variety of approaches to sex verification at different times since the 1930s. These have included visual tests, chromosome tests, and testosterone tests. The prevailing approach to the eligibility of trans women to compete in women’s events does not preclude those who are biologically male from competing in women’s sport, but it requires that their testosterone level remains below a certain threshold for a period prior to and continuously throughout their time competing in women’s competition (IOC, 2015). The requirement that trans, as well as intersex, women whose natural testosterone level is above the permitted threshold must undergo hormone treatment (i.e. androgen suppressive therapy) to bring their level below that threshold has been criticised as the unnecessary medicalisation of healthy athletes and a violation of the principle of beneficence in medical ethics. (Camporesi, 2016). Critics have suggested that athletes should not be required to meet certain physiological criteria to be eligible to compete in a particular gender category. Proposals sympathetic to this view have included that athletes should be allowed to compete in the gender category with which they identify (Davis and Edwards 2014); that trans women athletes should be allowed to compete in women’s sport but, to mitigate unfair advantage, should be subject to a handicap based on effective testosterone levels (Bianchi, 2017); and, finally, that eligibility should be determined by legally recognised gender (McKinnon and Conrad, forthcoming) 