Thanks ladies, that really helps to have something to compare to! I wasn't sure whether it was a small change that they are looking for or a big one, so it looks like it has room to almost double, all other factors aside. Last week it was 2.9.

3.2cm is amniotic fluid index, I wish it was deepest pocket! It is dropping fairly quickly, and I have been keeping really well hydrated too, whether it is making a difference or not I don't know, if I wasn't drinking so much water it might be lower, who knows...