You've probably heard people say that pretty much all newborns do is eat and sleep. While this statement is true, it's also wickedly deceptive. Newborns may sleep 16 to 18 hours a day, but not in large, several-hour blocks. Some babies awaken every 20 minutes, others every three hours. In other words, you can pretty much count on being awake with your baby while the rest of the world blissfully dozes on.
Because it takes time for a baby's brain to establish its circadian rhythm -- an inborn biological clock that creates sleeping and waking patterns -- she can't distinguish day from night and won't be able to sleep in larger blocks of time until 6 weeks or so.
And let's not forget the feeding factor. Newborns are hungry little creatures with tiny stomachs. Breastfed babies need to eat every two-and-a-half hours (breast milk digests very quickly); bottlefeeders about every four hours. Your best bet? Sleep when baby sleeps. If you breastfeed, pump milk so Dad can give baby her 3 a.m. feeding.