Some bottle-fed babies are perfectly happy with the first bottle-nipple you pop in their mouths, but others are a little bit pickier when it comes to their first set of utensils. And when you find one that works, it feels like a victory - and it is! That doesn’t mean it’s the last time you’ll be wrestling with bottle-nipple choices until it’s time to graduate her to sippy cups, though. There are two main reasons to switch bottle nipples - first is to replace nipples that need to be retired because of the wear and tear from your baby’s fearsome jaws, and second is to change the size of the opening on the bottle nipple to a faster flow as your baby grows.
Both latex and silicone bottle nipples can wear out after several months of use, particularly if they’re cleaned roughly, or with a brush, or if your baby’s teeth are a little early coming in and she's not inclined to play nice with them. Most bottle manufacturers recommend checking nipples for signs of wear when they’ve been in use about 3 months, although they can certainly last longer. However, if you notice them wearing out earlier, there’s definitely no reason not to take them out of use sooner.
Obvious signs of wear on both latex and silicone nipples are discoloration, pieces coming off, and changes in the nipples’ shapes. Worn out silicone nipples also look like they have cracks in them. Any of these signs is a good reason to retire a nipple. The less obvious reason, change in flow from the nipple, is easy to test by filling two bottles with warm water, fitting one with the old nipple and one with a new one, and watching the two flows against each other.
The problem with graduation from one flow-speed of nipple to the next is that there is no standardized level for what each type of nipple flow is. Instead, it changes between each brand, though each brand will give recommendations. Because every bottle brand’s nipple-flow is different and every baby is different, the guidelines for when to switch bottle nipples are almost completely arbitrary, and can only really be used as very rough guides.
The real thing that determines when your baby should move up to the next nipple-flow speed is of course your baby, and what she needs. She might be ready for the next nipple grade if she is sucking hard enough to collapse her bottle nipple regularly, or seems frustrated by how slowly the milk from her bottle is coming out. If, on the other hand, you switch up to the next grade of nipple and your baby has a hard time swallowing all of the milk as it comes out, she might not be ready to make the switch. In the end, if she seems happy with the speed that her dinner is getting to her, there really is no reason to change nipple grades at all.