Following your baby's cues is the best method when deciding to change the teat. The Natural Response Teat is available in teat flows 1 to 6. Enthusiastic drinkers usually need a lower teat flow since they are likely to suckle forcefully, resulting in greater milk flow. Teat 6 is more suitable for thicker liquids or babies who want a fast flow.
On the other hand, slow and steady drinkers will prefer a higher teat flow, as they tend to desire a lower milk flow.
As long as your baby is calm and comfortable while feeding, there is no need to change the teat. You do not need to raise the grade of the teat based on age. The cues given by your newborn are the best way to tell when they are ready for a higher teat.
For hygienic reasons, replace your teats every 3 months. Routinely inspect them before each use. Pull the nipple in different directions to inspect for any damage. If any damage or blemishes are present, do not use the teat and discard it.