Is it normal for my baby's sleep to get better and then worse?

Absolutely. Knock on wood before you start bragging to other parents that you're getting a full night's sleep, because there's a good chance you'll be woken up again soon.

"It's very normal for babies to sleep through the night at 3 or 4 months," says pediatrician Tanya Remer Altmann, editor of The Wonder Years: Helping Your Baby and Young Child Successfully Negotiate the Major Developmental Milestones. "You'll think this is fabulous, until all of a sudden your baby starts waking up again."

Altmann says congestion from a cold is a common culprit, as is pain from a tooth coming in, which can begin as early as 4 months. Also, too much stimulation during the day can make your baby overtired and restless. But once the cold has passed, the tooth is in, and your daily routines are normal, her sleep pattern should be back to normal, too, right?

Not necessarily. If you reintroduce habits from the first months of infancy, like feeding in the middle of the night and taking your baby out of her crib to comfort her, you might have trouble getting her sleep schedule back on track.

"If you go back to the routine from when your baby was a newborn, she'll go back to it and start waking up every three hours," says Altmann. "She'll want that time with Mommy and won't go back to sleeping through the night."

Altmann says it's okay to go in and pat your baby's back to settle her down, but don't be surprised if she cries when the patting stops. "Crying may be her way of settling down," she says. "It's hard to hear your baby cry, but remember you have all day to tell her you love her and that you're there for her."

If your baby's sleep gets derailed, either from sickness or a disrupted schedule, it will probably take anywhere from a few days to a week to get back on track. For a refresher, see our article on setting good sleep habits, or read what other parents wish they'd known about babies and sleep.