Prenatal sex hormone levels affect physical and behavioral sexual differentiation in animals and humans. Although prenatal hormones are theorized to influence sexual orientation in humans, evidence is sparse. Sexual orientation variables for 34 prenatally progesterone-exposed subjects (17 males and 17 females) were compared to matched controls (M age = 23.2 years). A case–control double-blind design was used drawing on existing data from the US/Denmark Prenatal Development Project. Index cases were exposed to lutocyclin (bioidentical progesterone = C21H30O2; M W : 314.46) and no other hormonal preparation. Controls were matched on 14 physical, medical, and socioeconomic variables. A structured interview conducted by a psychologist and self-administered questionnaires were used to collect data on sexual orientation, self-identification, attraction to the same and other sex, and history of sexual behavior with each sex. Compared to the unexposed, fewer exposed males and females identified as heterosexual and more of them reported histories of same-sex sexual behavior, attraction to the same or both sexes, and scored higher on attraction to males. Measures of heterosexual behavior and scores on attraction to females did not differ significantly by exposure. We conclude that, regardless of sex, exposure appeared to be associated with higher rates of bisexuality. Prenatal progesterone may be an underappreciated epigenetic factor in human sexual and psychosexual development and, in light of the current prevalence of progesterone treatment during pregnancy for a variety of pregnancy complications, warrants further investigation. These data on the effects of prenatal exposure to exogenous progesterone also suggest a potential role for natural early perturbations in progesterone levels in the development of sexual orientation.
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We thank Leonard A. Rosenblum for editing of the article, Carolyn S. Kaufman for research assistance during data collection and archiving, and Brandon Hill for assistance with literature searches.
This research was supported in part by US Public Health Service Grants DA 05056 to JMR and SAS, Grants HD 17655 and HD 20263 to JMR, Grant 9700093 from the Danish Research Councils to ELM. Some preliminary analyses of a portion of the complete data presented in final form in this paper were previously described in a thesis by Caroline Ripa, University of Copenhagen, 2002.
Conflict of interest
The authors declare that they have no conflict of interest.
Existing data from human research participants were used. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
At the time of data collection, informed consent was obtained from all individual participants included in the study.
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Reinisch, J.M., Mortensen, E.L. & Sanders, S.A. Prenatal Exposure to Progesterone Affects Sexual Orientation in Humans. Arch Sex Behav 46, 1239–1249 (2017). https://doi.org/10.1007/s10508-016-0923-z
- Sexual orientation
- Prenatal progesterone exposure
- Sexual behavior