There is this pregnant lady that I'm unsure about offering my seat to.
Why would you hesitate in offering her your seat? She's pregnant!
What if her sitting down causes her to go into labor? I don't want people to say that I'm the cause of that.
Leaving her standing seems like it would be more likely to cause her to go into labor. Offering your seat is just polite.
So now I have to be nice to people who I don't even know or care about? That's too much to ask for.
Not knowing her is not the issue, you should be considerate and let her have your seat. What if you had a condition or problem and needed somewhere to sit. Wouldn't you want someone to kindly offer you their seat?