Former NCAA track & field champion CeCe Telfer was ruled ineligible for the Olympic trials due to higher than normal testosterone levels.
Testosterone is a male sex hormone produced in the testicles that stimulates male secondary sex characteristics such as facial and body hair, deep voice, and muscular upper body build.
Biological women produce tiny amounts of testosterone in their ovaries.
Under World Athletics guidelines released in 2019, athletes can't compete for the USA in international women's events if their testosterone levels are high.
Testosterone levels must be below 5 nmol/L for a span of 12 months. In biological women, the normal testosterone range is 0.06 to 1.68 nmol/L.
Telfer, a Jamaican-born male-to-female transgender, is the first openly transgender male bodied person to win an NCAA women's title.
While a student athlete at Franklin Pierce University, Telfer first competed in the men's track and field division from 2016 to 2017 before transitioning, and winning first place in the women's 400-meter hurdles event in June 2019.
Helfer, who was raised by a single mother, is one of three children. The family moved from Jamaica to Canada when Telfer was 12.
Telfer's lawyer, David McFarland, said Telfer would respect the decision.