There is a much-cited "study" that you WILL be linked to in any debates on this issue.
This study was widely promoted in the press, there are hundreds of news articles about it. Big headline "study proves that trans people have brains more like their chosen gender, than their birth gender".
Here it is:
http://archive.is/HBRBMThe big problem is, this study was never published. They were planning to present this at the 2018 European Society of Endocrinology Conference, but it has since disappeared completely.
It does not show up on the ESoEC website. All links to this "study" simply re-quote the press release, which has no information about control groups or effect sizes (were they on hormones or not?).
The study is not on Dr. Julie Bakker's list of published studies:
https://orbi.uliege.be/ph-search?uid=U187615However, studies to the contrary DO exist. Here is a meta-analysis of every single study on this topic up until 2016:
https://archive.is/XpAsYThis confirms that females have MUCH different brains than males, in particular much smaller brains:
>Sex differences in the human brain have the same morphological characteristics observed in animal studies. Postmortem anatomical and in vivo MRI studies consistently report 9–12 % greater intracranial volume (ICV) in adult males than females as well as in children. Given the massive difference in brain size, would you really expect transgenders to be walking around with tiny heads? Obviously not.
This meta-analysis also confirms that transsexuals have brains more like their birth gender than their chosen gender:
>MRI studies show that ICV in adult and adolescent untreated homosexual MtFs is similar to male controls’. Moreover, GM, WM, and CSF volumes in homosexual MtFs do not differ from those of control males and are significantly greater than those of control females 
