A link between sexual orientation and prenatal exposure to progesterone has been identified in a new study published in the journal Archives of Sexual Behavior. Physicians often prescribe progesterone to support the fertilization process, prevent miscarriages or premature births, or to increase babies’ birth weights.

The study was a joint effort conducted by researchers at the University of Copenhagen, Denmark, and Indiana University, Bloomington, U.S. Using data from the U.S./Denmark Prenatal Development Project the researchers analyzed the sexual orientation of 68 subjects, 34 of whom (17 males and 17 females) were exposed to prenatal bioidentical progesterone. These subjects were matched on 14 physical, medical, and socioeconomic variables to a control group. The median age of all participants was 23.2 years. 

Sexual orientation, self-identification, and history of sexual behavior data was collected via a structured interview conducted by a psychologist and self-administered questionnaire.  

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The analysis showed that fewer subjects exposed to prenatal progesterone identified as heterosexual and more of them reported histories of same-sex sexual behavior and attraction to the same or both sexes. Twenty-point-six percent of the progesterone-exposed subjects labeled themselves as other than heterosexual. Compared to the untreated group, the chances were greater that by their mid-20s they had already engaged in some form of same-sex sexual behavior (in up to 24.2% of cases).

“The findings highlight the likelihood that prenatal exposure to progesterone may have a long-term influence on behavior related to sexuality in humans,” said lead researcher June Reinisch, Director Emerita of The Kinsey Institute.

The authors conclude that regardless of gender, exposure to progesterone appeared to be associated with higher rates of bisexuality. They stated that their findings warrant further investigation and that such studies could provide insight into the role of prenatal hormones on the development of human behavior, “in light of the current prevalence of progesterone treatment during pregnancy for a variety of pregnancy complications.” 

For more information visit Springer.com.