Surely that is called un fair dismissal

Unless it's your job to stop fights, I think it's illegal to get fired because of that... Congrats for your pregnancy :) !

it depends on what state. I live in Alabama and they can literally fire you for any reason or no reason at all

That sounds like bullshit! The most I would do to break up a fight is to holler at them to knock it off or throw cold water at them.

throw water on them

And he might get sued for discrimination.

unless your a bouncer... but still no.. they cant fault you for not stepping in when your about to pop as is.

sounds like they don't want to pay maturnaty leave.

Anyone that fires a pregnant women is looking at a automatic lawsuit... I think he just wants you gone now rather then having to wait for you to return after giving birth...

Worked as a corrections officer... Even at 8 months pregnant, I had to be able to perform the essential functions of my job, including potentially being involved in fights, to maintain my position as an officer. If this was an essential function of your job and you couldn't perform it, thats on you. If not, you might have a case against them.

my job is to make coffee haha :) I think I might

This is ridiculous... Clearly your employer had zero concern for your safety if they saw it was appropriate for a heavily pregnant woman to still be exposed to potential violence.
Couldn't they put you behind a desk or something?

Sounds like she works in an office, that's not quite the same as being a POLICE OFFICER.

I don't care if you're 7'6", 500 lbs, and can bench press an F150. You should not be expected to break up a fight unless you're some sort of security guard or peace officer.