Understanding Baby Growth Percentiles

It's not unusual for an infant to change percentiles between office visits. A baby grows by leaps and bounds between his first newborn exam and his first birthday. My daughter tripled her birth weight in her first year, leaping from the 50th percentile to the 75th percentile to the 80th percentile by her 12-month checkup.

However, if there's a sudden, extreme change, especially if your baby drops percentiles—for example falling from the 75th percentile to the 25th percentile—it may indicate a problem. "[Your child] should be following a curve, not deviating from a curve," Dr. Miller says. When a child's growth suddenly slows down, it may mean that illness, a nutritional problem, or a hormonal problem is affecting the ability to grow.

Keep in mind, though, that a lot depends on the accuracy of the measurements at each visit—and a kicking baby or wriggling toddler can make it difficult to get accurate measurements. And another point to remember: It's normal for growth to slow down after age one. While it's not unusual for babies to gain several pounds between office visits, your toddler might gain only four or five pounds total between 12 and 24 months.