The three 2016 Olympic medallists in the women's 800 metres were all excluded from the 2019 World Athletics Championships under the IAAF's testosterone rules. Caster Semenya, Francine Niyonsaba and Margaret Wambui all acknowledged they had a difference in sex development (DSD) which resulted in their bodies producing levels of testosterone above the limits set by the IAAF for women's competition. The IAAF rules stipulate such athletes must take testosterone-reducing medication in order to compete in women's races. Caster Semenya's appeal to the Court of Arbitration for Sport (CAS) against this rule was ongoing at the time of the World Championships. All three athletes declined to adhere to the IAAF's ruling and thus could not compete. CAS had previously made a decision in May 2019 to uphold the IAAF's rules on the grounds that they were discriminatory to athletes with a DSD, but that discriminatory action was "a necessary, reasonable and proportionate means of achieving the legitimate objective of ensuring fair competition in female athletics". Kenyan athletes, 800 m national champion Jackline Wambui and Linda Kageha, who was in the mixed relay team, were excluded from selection for Kenya as they refused to submit to a testosterone test. Because of the testosterone rule, 400 metres world No. 3 Aminatou Seyni competed in the women's 200 metres instead of women's 400 metres.