Whether you should wake a sleeping newborn for feedings depends on the baby's age, weight and overall health.
Most newborns lose weight in the first few days after birth. Until your newborn regains this lost weight — usually within one to two weeks after birth — it's important to feed him or her frequently. This might mean occasionally waking your baby for a feeding, especially if he or she sleeps for a stretch of more than four hours. Once your newborn establishes a pattern of weight gain and reaches the birth-weight milestone, however, it's generally OK to wait for feedings until he or she wakes up.
Most newborns need eight to 12 feedings a day — about one feeding every two to three hours. While waking up a sleeping baby might seem like a bad idea, frequent feedings early on are important for a couple of reasons:
Crying is a late sign of hunger. The sooner you begin each feeding, the less likely you'll need to soothe a frantic baby. Look for early signs of hunger, such as stirring, restlessness, sucking motions and lip movements.
Frequent feedings support early breast-feeding. If you breast-feed, frequent feedings will help you establish your milk supply.
Keep in mind that premature babies often have special nutritional needs. If your baby was born prematurely or you're concerned about your baby's feeding patterns or weight gain, consult his or her doctor for specific recommendations.