During the first two weeks of life and for some time after that, your baby's tummy will dictate her sleep routine. Breast-fed babies will need to eat every two to three hours; formula-fed babies every three to four. Infants are able to sleep for longer periods between feedings when they reach about 12 pounds.
1 to 2 Months
As infants get older, they naturally become more alert during the day and more sleepy at night. However, most babies at this age still need at least two 1- to 3-hour naps each day. All babies nap for different lengths of time, but if your baby sleeps longer than three or four hours during daytime naps, wake her up so that she will be sleepy at bedtime.
Your baby will probably start to skip one predawn feeding and nurse longer right before bedtime to stock up for the night. Keep in mind, though, that it's normal for babies this age to fuss or wake up several times during the night.
By three months, babies are ready to have a more formal bedtime. Now is the time to get your baby used to falling asleep after feeding, not during it. At first, this may be difficult, if not impossible, but getting him used to being placed in his crib while he's at least partially awake will make the bedtime routine easier as he gets older.
At this age (or 12 to 13 pounds) most babies no longer need to wake up for middle-of-the-night meals. This means they now can -- and do -- sleep through the night.
From The Parents Answer Book: From Birth Through Age Five, by the editors of Parents Magazine. Copyright © 2000 by Roundtable Press and G+J USA Publishing.