I hate this sort of know-nothing clownish crap. Medical practitioners absolutely should 100% be asking any female patient for this information always without exception no matter what as long as they are conscious. This is a quick attempt to check for:
1) Possible pregnancy. Many drugs can cause pregnancy complications and harm the fetus. Also lots of drugs can cause vastly different reactions when a woman is pregnant.
2) Anemia. Very common in women and very dangerous when conducting emergency medical treatment (and in general). No recent menses == very very high chance of anemia.
Anyone who does not ask an injured woman the last time she menstruated is engaged in actual fucking malpractice because if you get it wrong YOU HARM YOUR FUCKING PATIENT.
As for the poster, she is a goddamn idiot. It’s amazing people just post without knowing anything.
It’s strictly a polite way of asking if you’re pregnant – I always answer it as such.
That is the main purpose, yes. And of course it’s medically important to know that, so I’m unsure why it’s treated by so many as oppression.