I changed to no. 2 (NUK no.2 medium hole - for milk) already since my b ate 4 oz/meal in the past 3 weeks. So, I decided to change to no.2 to see if it works. At the beginning, he ate 4 oz/meal still. So, I brought 2 no. 2 large hole and see if it's the problem of 奶咀. However, he doesn't like the large hole and made him "俗"親. So, I use the medium hole. Later on, he ate 6oz/meal even use the medium hole.
Actually, I have both (Pigeon & Nuk). I guess that they are the medium hole for 6mons under. My BB is very comfortable for them. They seem really good for her. But I find the Nuk have the 6mons+ that I'm not sure need to change or not? Even she try to use the large hole, it really make her "俗"親. So, I really don't know we must or need not to change the size ! Can we keep to use the old one?
If the baby feels comfortable & drinks well, I suggest not to change to a bigger size. BB will adjust by herself. She will let you know when she wants a bigger one.