Why would you want to announce the birth anatomy of a person you just met?
This is where I need to mention that in addition to the fact that you don’t know this about a person you just met (I’ve met several trans people that you’d never guess were trans) it’s also really rude to refer to a person by their birth anatomy and not by their current social gender.
Now, there are contexts where someone needs to know that. Mostly those are medical contexts. My son’s new doctor asked (on a form) for his sex assigned at birth, his legally sex, and his gender and pronouns. And they need all of those. They need his legal sex for interacting with insurance companies. They need his sex assigned at birth to know what parts he has, and of course they, like everyone else, need to know how to address him.
So “AMAB” works fine for these limited contexts where it’s actually needed.
I would discourage you from mentioning that about the girl you are about to have a first date with, however.
(edited to correct typo)