The first few weeks with your baby are a lot like boot camp. You get next to no sleep, you find yourself frequently surrounded by screaming, and you worry that you'll do something wrong.

Your infant's a bit stressed too. She may feel as if she's made a wrong turn somewhere: Instead of swimming in warm comfort, she's suddenly sleeping on a cold, hard bed...surrounded by bars. Fortunately, a baby is sturdier than you think. (You are too, but that's another story.)

"Most infants are born without any complications," says Joshua Copel, M.D., chief of high-risk obstetrics at Yale New Haven Hospital, "and their immune systems are made stronger with maternal antibodies [infection-fighting proteins] passed on during pregnancy." And, as moms soon realize, the more you know about your baby, the more you can relax and enjoy. To help you get there just a little sooner, here's a no-worries guide to the most common newborn health concerns.

He sleeps a lot!

The average newborn snoozes for 16 to 18 hours a day, waking up every one to four hours for a feeding. He won't establish a pattern of sleeping during the night more than during the day for a month or more. If you're concerned that he's lethargic rather than simply sleepy, check his diapers. "A newborn should wet a minimum of six to eight diapers a day," says Claibourne Dungy, M.D., a pediatrician at Children's Hospital of Iowa, in Iowa City. "Anything less and he may be dehydrated." That can be self-perpetuating: "The less a baby eats, the less energy he has to eat."

Call the pediatrician if: your newborn sleeps for longer than six or eight hours at a stretch, is hard to rouse, skips more than three feedings, has difficulty latching on to the breast or bottle, or has a temperature below 97°F or above 100.4°F.

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