When this woman is unsure if she should've gotten up for a pregnant woman, she asks Reddit:
Okay so I (F21) was driving back home from my parents place the other day. They live a 2h train ride away and I spent several days there, so I took my cat with me. He's used to the train rides and usually just sleeps thru.
I also usually have the carrier on the seat next to me, but whenever the train gets full I put it on my lap so other people can sit.
So this very pregnant woman comes in (I'm not good with guessing months but she was pretty big so I assume at least 6 months?), the train is full so naturally I took the carrier on my lap and offered her the seat next to me.