“PRENATAL exposure to progesterone affects sexual orientation in humans”. A bold and unequivocal-sounding title for a scientific paper. And certainly important if true. But is it?
The study claimed to show that women given extra progesterone during pregnancy, routinely prescribed to prevent miscarriage, bleeding or premature delivery, have children who are “” to later identify as bisexual.
It would be a landmark finding, allowing us to also ground in biology the established social science contention that sexuality has more dimensions than straight and gay.
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We suspected that exposing a fetus to strong hormones can shape sexual orientation. But there are no animal models of sexual orientation, and doing this kind of experiment in humans would be deeply unethical. The next best thing would be a retrospective analysis looking at a birth cohort exposed to a specific hormone “in the wild”. And that’s what this study did.
June Reinisch of the Kinsey Institute in Indiana and her colleagues trawled a public database containing records of more than 9000 pregnancies in Denmark between 1959 and 1961. They identified women who were given a progesterone-mimicking hormone by the trade name lutocyclin to prevent miscarriage.
Lutocyclin did seem to have mild effects on sexual orientation: later in life, exposed individuals were five times more likely to self-identify as non-heterosexual, and were more likely to report relationships with the same sex, than unexposed controls.
Two criticisms of the study are familiar: both its size and the effects on sexuality are small. Just 34 people – 17 men and 17 women – were exposed to the hormone in utero. One of the men identified as homosexual, two as bisexual and two as “don’t know”. Of the women, two identified as bisexual.
“There is a question about what hormone the trade name of the drug really referred to”
Not that the study is without value. “I think it’s a real effect,” says , a neuroscientist who in 1991 claimed a specific brain region was smaller in gay men. “The study seems well done, and supports the idea that the prenatal hormonal environment affects sexual orientation,” he says.
of Emory University in Georgia feels similarly. “This is a very unique sample, and a real strength is that the subjects only received lutocyclin,” he says.
However, Levay and Wallen flag a concern: there is a question as to whether, in the 1950s, the trade name lutocyclin referred to progesterone. They wonder if it could have been ethisterone, a testosterone derivative invented in 1939. A methyl grouping enables it to act like progesterone, but it almost certainly retains the ability to act like the masculine hormone, testosterone, which is also implicated in influencing sexuality through exposure in the womb.
Reinisch says she is “certain” it was progesterone, and if she is right, there could be repercussions. If women conclude that progesterone might affect the sexuality of their child, they may avoid a treatment that could rescue an otherwise doomed pregnancy.
While this study adds to the evidence that extra hormones during pregnancy may alter characteristics, until the result is replicated with a hormone that everyone agrees is progesterone, it is by no means the last word on the origins of bisexuality or the effect of progesterone in pregnancy.
This article appeared in print under the headline “A sexuality hormone? It’s not that simple”
