Yes. Our instructions note to use a level 2 nipple because doctors typically recommend that nipple size for babies 4 months and older. You can use a preemie sized nipple, but there's a small chance (less than 10%) the nipple may become clogged depending on if your baby has enough sucking power. Should that happen, try adding a little warm water and shaking the bottle a little harder. You can also try a level 1 nipple if your baby has developed a good latch.