When my son was born, they told me to wake him every three hours. And he was in the NICU for a week (not related to weight or other feeding issues) and they woke him every 3 hours. Hospital policy, I thik. But next time I have a baby, I won't be waking him every 3 hours!! Like someone else said, you probably wouldn't want to go more than 5 hours. And I think that more frequent feedings of newborns are related to less jaundice, or something like that. So if your baby wakes up to eat, then just let her sleep. But if she just sleeps and sleeps and sleeps, you might want to ask yoru pediatrician about waking her up.