A treatment for a rare birth disorder has been found to have a controversial side-effect: It evidently reduces the likelihood that treated girls will become gay.

Rights groups and medical experts are coming out against the treatment, saying it amounts to "engineering in the womb for sexual orientation."

The rare condition known as congenital adrenal hyperplasia causes girls to develop ambiguous genitals and facial hair, as well as failure to menstruate. Studies have suggested that "biological and psychological factors" result in individuals with the condition being more likely to be gay.

Now a new hormone treatment, reported on by Raw Story in June, has been shown to reduce the condition's effects, while at the same time reducing the likelihood that the treated person will be gay.

The Los Angeles Times reports that activist groups and doctors fear what the treatment may mean for sexual orientation rights.

The treatment could lead to "engineering in the womb for sexual orientation," Alice Dreger, a Northwestern University medicine and bioethics professor, told the Times.

Other medical experts have joined gay-rights groups in opposing the treatment. The Times reports:

Dreger and critics — which include the National Center for Lesbian Rights, Advocates for Informed Choice (an organization that works to protect the rights of people with intersex conditions), and some pediatric endocrinologists and parents of children with the condition — say far too little is known about the safety of the hormone, the steroid dexamethasone, when used prenatally. They say it should be used sparingly, in closely monitored clinical trials, or not at all. They're even more concerned that some doctors might tell parents that a reduced chance of homosexuality is one of the therapy's benefits.

Much of the controversy surrounding prenatal dexamethasone treatment, as it is known, has focused around Dr. Maria New of New York's Mount Sinai Medical Center, whose studies of the treatment have concluded that it effectively reduces the symptoms of CAH -- and at the same time reduces "masculine behavior" among girls treated for the condition.

New found, for instance, that treated girls were more likely to want to bear children than those who were untreated . Her research has given rise to fears that parents will try to use the treatment to ensure they have "feminine" daughters.

There appear to be risks involved with the treatment. Tests on animals showed the treatment "to cause an increased risk of high blood pressure, plus changes in glucose metabolism, brain structure and brain function, leading to memory problems," the Times reports.

This September, a consortium of medical experts will lay out new guidelines for the treating of children with CAH. The guidelines are expected to label the treatment as "experimental" and recommend instead the traditional method of using corrective surgery to fix the symptoms of CAH. But the consortium is "not expected to discourage research on the treatment," the Times reports.

Indeed, the treatment seems unlikely to go away, if only because of the positive effects it has on the symptoms of CAH and the scientific curiosity it has piqued with its controversial side effect.

Ken Zucker of Toronto's Centre for Addiction and Mental Health told the Times, "Some people refer to girls with CAH as experiments of nature because you've got this condition and you can take advantage of studying it."

About one in 15,000 births -- or a few dozen per year in the US -- is affected by CAH.