Falling asleep on feeds, taking longer then usual to feed, general irritability when feeding....theres probably more though. I dont really think theres a need to change if you think LO is ok with the usual ones, we didnt anyway.
We swapped our LO to stage 2 teats at 3 weeks old as we changed her milk to comfort milk as it was thicker than normal stage 1. Shes still on the same ones now.