I am really not sure if I am bu, pre pregnancy I would offer my seat to anyone who looked like they needed a sit down, older people, small children pregnant people and obviously disabled people.
I'm 7 months pregnant and have an obvious bump, I work in Stockholm and travel on the tube and busses for around 3 hours a day. I carry heavy bags around full of teaching resources (slightly irrelevant) not once has someone offered me their seat, people often push past slow moving me to grab a vacant seat, occasionally I have had people gutting when I ask them to move their handbag/small dog/feet from a seat so I can sit down.
I know pregnancy is a choice and I'm not ill I'm just pregnant, I do have very painful hips and back by the middle of the day and when I'm standing feel like I'm about to wet myself constantly.
I wonder if it is like this in all countries? I am happy to accept I'm bu if that's the case.