"...mammalian sex determination is more directly under the control of a single internal event: fertilization. Under normal conditions, the direction of sexual development is initiated and determined by the presence or absence of a Y chromosome."

The gender discussion is of course different.

Tim, aren't XY or XX, thus sex determined at conception? I don't want to defend a cruel, petty, vindictive, pandering EO, I'm just not sure it is subject to this specific criticism. Hopefully someone smarter than me will jump in and tell me I'm wrong.