Understanding Baby Growth Percentiles

Even if your baby falls at the extreme high or low end of the chart, there's usually no cause for alarm. "A healthy child can fall anywhere on the chart—even above the 97th percentile or below the 3rd percentile. They're just at the edges of the norm," Dr. Miller says.

What's important is that the height and weight percentiles should fall in roughly the same neighborhood. If your daughter is in the 10th percentile for weight and the 25th percentile for height, everything's probably fine and she just happens to be petite. However, if she's in the 10th percentile for weight and the 90th percentile for height, your doctor might become concerned and monitor her nutritional intake more closely.

Keep in mind that, while nutrition is important, genetics plays a huge role in how your baby grows. According to Dr. Miller, a child will usually mirror the growth pattern of the same-sex parent. That means if you were tall and thin at 18 months, your daughter probably will be, too. And if you're concerned that your toddler son is on the short side, ask your mother-in-law to dig out your husband's baby photos. Chances are, he looked the same at that age. Like mother, like daughter. Like father, like son.