The soft, naturally shaped AVENT nipple makes it easier to switch between breast and bottle feeding, and promotes healthier, active feeding. The built-in valve flexes with baby"s natural feeding rhythm and lets baby control the flow of milk, which can help reduce overeating and spit-up. The valve also prevents a vacuum and pushes bubbles out of the milk, for less air in baby"s tummy. This reduces colic and gas after feeding. Newborn Flow Rate is most like breastfeeding flow; ideal for breastfed babies of all ages Slow Flow Rate is ideal for breastfed babies of all ages Medium Flow Rate is ideal for babies 3 months + Fast Flow Rate is ideal for babies 6 months + Avent makes it easy for you to breastfeed, bottle feed or combine the two. The Avent Natural Feeding System gives you the flexibility and efficiency you need to choose what feels right for you and your baby from birth and beyond. Avent is the only feeding system that is clinically proven and doctor recommended. From the beginning, using the Avent Natural Feeding System is easy and convenient. As a fully interchangeable system, Avent makes it easy to transition effortlessly into new stages of your baby"s development. With the exception of the Tempo system, all Avent nipples, bottles, cups, spouts and handles are interchangeable, so you can customize you baby"s feeding and transition them with ease. At home or on the go, Avent fits naturally into your busy life by giving you everyday conveniences you need to make the best feeding choices, every step of the way.