Sexual differentiation of the mammalian brain starts during fetal development and continues after birth (Kawata, 1995; Swaab et. al., 2001). It is hypothesised that in humans, in common with all other mammals studied, hormones significantly influence this dimorphic development although, at present, the exact mechanism is incompletely understood. It is also postulated that these hormonal effects occur at several critical periods of development of the sexual differentiation of the brain during which gender identity is established, initially during the fetal period, then around the time of birth; and also post-natally. Factors which may contribute to an altered hormone environment in the brain at the critical moments in its early development might include genetic influences (Landèn, 1999; Coolidge et. al, 2002) and/or medication, environmental influences (Diamond et. al., 1996; Whitten et. al., 2002), stress or trauma to the mother during pregnancy (Ward et. al., 2002; Swaab et. al., 2002).
http://www.gires.org.uk/Web_Page_Ass...ion_signed.htm
You seem to be making a point about biological sex. However, this is not the same as Gender. One's gender is part of their personal identity, the way we understand ourselves on a fundimental level. I'm not sure if you are making a point that Gender Dysphoria is has no biological cause or if you are stating that the male/female sex can be modified during gestation.