Why has sport kept testing who counts as a woman?

Sport has kept testing who counts as a woman because women's events exist, and officials have wanted to be sure that only women compete in them. The practice began in the 1940s with "femininity certificates" provided by a physician, and moved on to visual inspections, physical examinations, chromosome tests and testosterone tests. The tests were designed to make sure athletes competed only as their sex, but in practice they mostly ended up excluding intersex athletes from women's sport.

Each method has had its turn. Avery Brundage, a future IOC president, asked for a system to examine female athletes during or shortly after the 1936 Games, and at first women were asked to parade nude before a panel of doctors. From 1958 to 1992, all female athletes at IAAF and IOC events had to pass a test: cells swabbed from inside the cheek were checked for evidence of XX chromosomes. In 1985 the runner Maria José Martínez-Patiño failed that test, two years after passing it. She was told to retire quietly, as was common, and refused, which drew immense public scrutiny.

The trouble is that biology does not sort neatly. Some people are not unambiguously female or male, not all of a person's cells share the same genotype, and other atypical genetic conditions exist. Towards the end of the twentieth century, sporting bodies dropped chromosome tests and switched to hormone tests, which meant writing rules on hyperandrogenism, naturally higher testosterone in women. Those rules have been fought over in public and in court ever since.

The best-known case is Caster Semenya's. After she won the 800 metres at the 2009 World Championships, she was made to undergo sex testing, a decision that sparked controversy in sport and in South Africa. Later reports said she has a difference of sex development, 5α-reductase 2 deficiency, with natural testosterone in the typical male range. The newest turn came in March 2026, when the IOC announced that from Los Angeles 2028, the women's category would be limited to athletes identified as female at birth, checked by a one-time sex test.