Pls at least acknowledge

The thing abt giving up seats on the mrt or bus...to me, i will give up my seats to pregnant woman, elders, and people carrying children on their arms but not kids...so far, the people that i gave up my seats to, will say thanks or at least smile to me...

However, this evening on the way home, i gave up my seat to a pregnant woman after just sitting for 2 stations...she didn't even smile or thank me...so i wonder, is it really my obligation to give up my seat to her? i'm also tired after working the whole day, i'm wearing heels and my bag is not really light...but i still gave up my seat to her...she shd at least smile to acknowledge my action (not that i didn't smile to her - i did!)...

Just want to say, everyone has a right to the seat, give people the due respect when they gave up their seats to you because you need or seem to need the seat more than them...