Hi ladies, it all depends on what kind of bottles you are using. If you are using the glass type, you don't need to change unless your broke it. Of course lah.
However, if you are using the plastic type, then you have to change it once every quarter. If KS a bit, change it every 2 to 3 months. This is because plastic bottles tend of the hairline scratch that you can't see it. Chemical will leak into the milk. Especially we steam and stem and steam it.
Same for teats. For hygiene purposes too.