Sexual orientation er a result of many factors, perhaps progesterone is one of them, according to a new study. (Photo: Shutterstock)

Possible link between hormone treatment and sexuality: study

In a study of 34 people, some adults were more likely to identify as homosexual or bisexual if their mother took progesterone while pregnant. But is just one of the many factors that might influence our sexuality, say scientists.

Pregnant women who take progesterone as part of hormone therapy may increase the likelihood that their child will identify as bisexual or homosexual.

Scientists have discovered that people whose mothers took progesterone while pregnant identify as heterosexual less often than those whose mother did not receive progesterone treatment.

Adult children of mothers who received hormone treatment are more likely to have thought about having sex with someone of the same sex than those in a control group, shows the new study.

“There are clear indications that they’re more open for having sex with someone of their own gender. The study also underpins a general point that we should be more careful with the type of medication we give to pregnant women, because it takes very little to influence the foetus,” says co-author Erik Lykke Mortensen from the Department of Public Health at the University of Copenhagen, Denmark.

The new study is published in the scientific journal Archives of Sexual Behaviour

Sexuality is more than just hormones

Mortensen emphasises however, that sexual orientation should not be considered as a mere side effect of progesterone treatment in pregnant women.

Progesterone is found naturally in the body. And pregnant women run the risk of miscarriage if their level of progesterone is too low. Here, progesterone treatment can reduce this risk.

Many other things also influence sexual orientation, says Mortensen.

“Progesterone is just an example of the interaction between biology, environmental factors and development. No one is suggesting that something as complex as sexual orientation can be determined by a single hormone,” he says.

Read more: Contraception influences sexual desire in committed relationships

Studied just 34 people

The new study includes data from 34 Danes (17 men and women) born at the University Hospital in Copenhagen, Denmark, between 1959 and 1961, as part of the Copenhagen Perinatal Cohort.

All of them were born to mother’s who had been treated with progesterone (and no other form of hormone treatment) during their first two trimesters in order to avoid a miscarriage.

When the children were approximately 23 they were asked to complete a questionnaire about their sexual orientation and interviewed by a psychologist. The results were compared with those from another group whose mothers were not treated with progesterone.

Read More: Love matters more than genes for children with same-sex parents

More people identified as gay or bisexual after hormone treatment

The results showed a greater tendency, especially among men, to identify as gay or bisexual if their mother had been treated with progesterone. This was around 20 per cent (five men and two women) compared to zero in the control group.

When asked if they had ever been attracted to a member of their own sex, approximately 30 per cent said yes (six men and four women), compared to six per cent in the control (zero men, two women). Almost eighteen percent said they were currently attracted to both sexes (three men and three women), compared to three per cent in the control (zero men, one woman).

Between 14.7 and 24.2 per cent said that they had some kind of sexual relationship with a member of their own sex, which compared to 0 to 9.1 per cent in the control group. Here sexual contact ranged from being fully undressed (17.6 per cent), intercourse (14.7 per cent), going to bed together (17.6), or masturbating in front of someone (24.2 per cent).

Read More: Ugandan anti-gay laws have not curbed homosexuality

Larger studies needed to see a correlation

Professor Anja Pinborg from the Department of Clinical Medicine at the University of Copenhagen, Denmark, and a doctor at the fertility clinic at Hvidovre Hospital, thinks that more studies are needed before they can conclude whether there is a link between taking progesterone while pregnant and the child’s sexuality.

“I can see that the topic is interesting but I think that there’s too large uncertainties in the relationship between progesterone treatments and sexual orientation in this study with only 17 people in each group,” writes Anja in an email to ScienceNordic.

Mortensen agrees, but adds that “on the other hand this is the biggest study of it’s kind and there is a statistically significant relationship. In addition, the test group and the control group are matched much more carefully than usual.”

Read More: Same-sex marriages are on the rise in Norway

Results are not surprising

Mortensen is not surprised by the results.

“It’s an old, but related idea, that sex hormones have an influence on how we develop as men and women and our sexuality. From that perspective, perhaps the results aren’t so surprising,” he says.

The primary difference between men and women are their hormones, which with the help of the y-chromosome are excreted in the man’s or the woman’s body, he says.

So when a foetus is exposed to hormones it may impact the hormonal processes, which influence our sexual orientation, says Mortensen.

But there is still more work to do to incorporate the many other interacting factors which influence our sexuality, he says.

“Even though we can see an effect, it’s not clear in what direction, and we need more studies and larger studies before we can say with certainty how progesterone during pregnancy plays a role and what other factors are involved,” says Mortensen.



Read more in the Danish version of this article on


Translated by: Catherine Jex

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