Furthermore, "what sex are you" can be different for the same exact trans person in a doctor's office depending on how this information is being used.

What letter do I have on my ID? And which ID - state vs federal vs birth certificate vs social security
What letter does my insurance have on file for me
What hormones do I run on now
What hormones have I run on in the past
What organs do I have now
What organs have I had in the past
What pronouns do I want people to talk to me as

All mixed with the question of "will I still be treated with care and respect if I out myself to strangers?"

And that's a big fuckin unknown scary question for any trans person going to a doctor for the first time when they hand you a clipboard with "what's your sex at birth"?

Right, but if you were born without them, then they aren't a risk

Good point, but "sex at birth" has a ton of medical implications, and it would take a LOT more effort (which is certainly called for) to list all the critical things one would need to specify.

e.g. "have you ever had ... ovaries, testes, prostate, breasts, ..."

I guess it was a bad idea all along to assume stuff from "assigned sex at birth", and we, as medical professionals need to rethink how we determine risk and how we ask

Also, like, I could guess but I don't know for sure I've got ovaries. If that's important for medical diagnosis, surely I'm not the one who should be figuring it out!

I will lie every single time because my assigned sex actually says nothing about my current body.

My hormones are female. My genitals are female. My body is female.

If you treat me as my sex assigned at birth, you could actually kill me.

So, I hope like crazy they aren't lying, because that would mess with testing and diagnostics in a bad way