When new parents come into my office for their baby's first checkup, I tell them that pediatrics is a partnership between parents and doctor, and each person plays an important role. Parents need to be keen observers and accurate reporters, while a doctor must use the parents' observations to help make the right diagnosis and prescribe proper treatment.

During the first year, you'll learn a lot about how your baby communicates. Before you realize it, you'll be an expert at differentiating hungry cries from sleepy ones and wet-diaper wails from I-want-to-cuddle whimpers. You'll know your baby's sleeping and eating patterns, and the sparkle in her eyes that comes when she's happy.

Understanding when your baby is sick requires knowing her when she's well. Often a change in behavior will be the first symptom you notice, but it helps to know the signs that pediatricians look for as well. Here, a guide to some of the most common illnesses that babies encounter during the first year.

Contributing editor William Sears, M.D., is the author, along with his wife, Martha Sears, R.N., of The Baby Book.

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