The document states that in the women’s category competitions of the Olympic Games or any other event of the Olympic Committee, only women, that is, those with female biological sex, may participate, both in individual competitions and in those carried out by teams.

To determine who can compete in the female category, a genetic test will be performed to detect the presence of the SRY gene, which determines that the person is male.

It is a simple test that is performed by collecting saliva, with a buccal swab or with a blood sample, which is done once and serves for life.

In this way, athletes with a negative test for the SRY gene will be able to participate in women’s competitions.

Exceptions to this rule include athletes who suffer from Complete Androgen Insensitivity Syndrome or other rare disorders of sexual development (DSD), who do not benefit from the enhancing effects of testosterone.

Athletes with a positive SRY test result will be able to compete in the male or mixed categories.

The working group that prepared the document reviewed the latest scientific evidence and concluded that  the male sex has a competitive advantage in all sports over the female sex in strength, power, and endurance. 

According to the IOC, this new policy protects equal opportunities for female athletes in competitions, promotes Olympic values, and increases the visibility of the female category.

Background

In September 2025, the United States Olympic Committee  already banned the participation of “trans women,” that is, biological males who had transitioned to the female gender, in women’s competitions. 

Until now, the International Olympic Committee allowed each sports federation to decide whether trans athletes could compete in international events.

Previously, both  World Aquatics  and  World Athletics had already banned trans women from competing in women’s categories.

In 2023, Sebastian Coe, Olympic champion and director of World Athletics, stated that “we must maintain fairness for female athletes above all other considerations. We will be guided in this by the science surrounding physical performance and the male advantage that will inevitably develop in the coming years. As more evidence becomes available, we will review our position, but we believe that the integrity of the women’s category in athletics is paramount.”

Bioethical assessment

The conflicts arising from the implementation of the tenets of gender ideology stem from a lack of scientific foundation. The confusion created in the treatment of the concepts of sex and gender, promoting their complete dissociation, generates unfair comparisons when mere desire ignores the biological condition that every human being possesses, specifically their sexed nature.

The sexual configuration of individuals of the human species, as in many other species, is determined by the genetic combination of the genomes of the male and female gametes at the moment of fertilization. Thus, from the zygote stage—a single-celled individual of the human species—sex is defined not only by the presence of the SRY gene (Sex-determining Region Y), located in region 1 of the short arm of the Y chromosome, and primarily responsible for the development of male sexual characteristics in mammals.

This gene determines the masculinization process in the seventh week of gestation. But other genes are also involved in sexual differentiation, such as the Tfm gene, located on the X chromosome, which encodes the receptor for male hormones, or the ODF region of the X chromosome, which promotes ovary development and inhibits testicular development.

In embryonic development, the activation of certain sex-specific genes leads to the silencing of their counterparts of the other sex: the H19 gene is silenced on the chromosome of paternal origin and the Igf2 gene is silenced on the maternal one (epigenetic mechanisms).

Other genes, located on different chromosomes, are involved in sexual differentiation. For example, the gene that codes for the synthesis of anti-Müllerian hormone by Sertoli cells in the testis is on the short arm of chromosome 19, and the  Gadd45g gene , located on chromosome 9, is crucial for masculinization and interacts with the SRY gene.

In addition, another gene, WNT4, located on the short arm of chromosome 1, encodes a protein important for the formation of the female reproductive system, kidneys, and several hormone-producing glands. The protein it encodes regulates the formation of the Müllerian ducts, which give rise to the uterus, ovaries, fallopian tubes, cervix, and upper part of the vagina.

Sex-differentiated gene expression also plays a fundamental role in sexual development. One study  identified  approximately 6,500 human protein-coding genes that react differently in males and females. This study establishes that sexually dimorphic traits result primarily from the differential expression of genes present in both sexes. These genes may be subject to different, and even opposing, selection constraints in the two sexes.

From all this it follows that the genetic heritage that defines sex in humans is complex and multifactorial, with a multitude of genes involved, which constitute the two phenotypic expressions male and female.

Various alterations in the genetic configuration that defines sex can lead to disorders of sex development (DSD), resulting in incomplete development of the gonads or phenotypic characteristics of both sexes, which in any case constitute rare exceptions to the biological norm of sexual differentiation.

Thus, as we have  previously published , these infrequent alterations in sexual development must be differentiated from the transition processes in transsexuals, requiring individualized analysis and assessment.

Ignoring the biological differences between the sexes, which are very stably encoded by large sections of our genome and responsible for the differences in their phenotypic expression, opens the door to discrimination in sports competition, where some developmental characteristics show significant differences.

This should not be related to discriminatory procedures, because what is discriminatory is demanding the same performance under very different physiological conditions, something that has always been avoided by creating male and female categories in sports competitions where these differences significantly affect performance.

Julio Tudela. Ester Bosch. Bioethics Observatory. Institute of Life Sciences. Catholic University of Valencia