TAKING pills for slimming and thyroid problems during pregnancy may increase the possibility of bearing lesbian daughters, a study has revealed.

Researchers studied thousands of pregnant women to study the effect of prescription drugs on their babies and discovered that the drug thyroxine, used to treat thyroid deficiency, and amphetamine-based slimming pills appear to influence homosexuality among female children.

The results show sexual orientation is affected by prenatal rather than social factors, with mothers of homosexual girls proving eight times more likely to have taken those pills — most noticeably with daughters whose mothers took them during their first three months of pregnancy.

Professor Lee Ellis and his team at Minot State University, North Dakota, compiled the study using the mothers of more than 5,000 students. They discovered thyroid pills were taken by 5.2% of the mothers of lesbians but by only 1% of mothers of female heterosexuals. Slimming pills were taken by 2% of mothers of lesbians but only 0.2% of mothers of heterosexual children. The findings will appear in the journal Personality and Individual Differences, next month.

They also discovered that women who suffered prenatal stress were more likely to have a male homosexual child.

The report concludes: “The most noteworthy findings were that if prenatal therapeutic substances affect offspring sexual orientation, the effects are mainly confined to female offspring and are limited to the first trimester of pregnancy.

“In particular, mothers of the female homosexuals in our sample were significantly more likely than mothers of female heterosexuals to have taken diet pills and thyroid medications during pregnancy.”

It also revealed that some drugs can have the opposite effect — mothers of heterosexual males were 70% more likely to have taken pills to combat nausea than those of gay men.

Ellis said: “This was the first study in that area — looking at the effect of prescribed drugs — we found no evidence of male homosexuality but it did tie up to lesbianism. We were interested in prenatal stress but thought we should look at other prenatal factors and this was not what we expected to find but it was very clear.”

He added that the numbers taking the drugs were small and a larger study should be undertaken.

He said: “It took us a long time to do so I hope someone else can take it further and recompile the data.”

Professor Jim Dornan, vice-president of the Royal College of Obstetricians and Gynaecologists, called it an “very interesting finding which definitely deserves further study”.

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