It depends on whether you’re feeding formula or bm. My LO was on bm so she only switched to size 1 at 5mo. Skipped size 2 and switched to Size 3 at 12mo, then size 4 till now (22mo, on formula). If baby is taking too long to finish a bottle (like every feed), it’s time to upsize 😊.
You don’t have to change just because it’s said so on the box. I waited for my baby’s cue, eg, easily frustrated when drinking. And I have 5 bottles, so I changed one first to see if it helps and whether baby is drinking smoothly from it.
Wait for baby’s cue. My baby is 2 months old and still using 0M+ teats. You will notice baby drinking slower and slower and start to get very tired of sucking the teat then you know it’s time to change to a faster one 😅
Depends on the age of your baby or whenever baby's ready. For newborn will be 0 then 1 month later will be next teat size. Then Ill change to next size whenever ready or whenever baby prefer faster flow.
I change my LO’s teat at 3month old. I introduce to him in the day time when he is most awake