Like piranha on fresh meat, the transgender community has taken to embracing the brain hormone wash theory for causing transgenderism, but they would be wrong. It is only a theory that evolved from inconclusive research performed on dead transgenders.
This is a quote from an article—
Recently, researchers have looked into the possible causes of transsexualism. One study has found that on examination of the brains of deceased transsexuals, the brains resemble the sex that they always insisted they were. This would indicate that one's feelings of being male or female are set in the brain from birth and cannot be altered. It is hypothesised that these feelings could be due to abnormalities in hormones before birth.
Now some think the brains of the deceased transsexuals might have been changed over time by the hormone therapy itself and not connected to any supposed pre-natal hormone wash in the womb. That, too, is just a theory. More from the article—
The research is not conclusive, though. Only a very small number of brains have been examined. Also the differences could be from the way that a brain is used, or from the administration of hormones to transsexuals during therapy. Other researchers hypothesise that transsexualism may be caused by an upbringing: which was either dysfunctional or where gender was not emphasised enough. Neither of these theories have been proved conclusively.
The brain hormone wash in the womb has not yet been proven to be true; it’s still a theory without factual proof. You can say that transgenders are who they are because of a brain hormone wash, but that has not yet been proven to be true.
Reference article: http://www.h2g2.com/approved_entry/A830413