Of all the biological functions that autogynephiles fetishize, the fetish of menstruation and period cycles has to be the weirdest one out there. The fantasy of having a physical female body and what comes along with it (i.e. breasts and a vagina) is easy to understand because they are heterosexual men and straight men tend to place an emphasis on the physical appearances of a woman. But the period one doesn't make any sense because it's not even a remotely sexual function.
Why would any sane guy want to experience the immense physical pain and discomfort that's involved in menstrual cycles such as period cramps and fevers? Although I can't speak on behalf of women as I'm a man, every female in my life has told me the struggles and difficulties that occur whenever the time of the month comes. It doesn't make the poor women who experience them feel very sexy either. If MTFs ever had an actual period and had to deal with all the unpleasant shit that it entails, they'd probably blame it on the "TERFS" and "transphobia".