When Brenda Nixon of Mount Vernon, Ohio, was told that her daughter was only in the 5th percentile for height and weight, she was concerned. When – after several pediatric visits – her daughter was still on the low end of the scale, the doctor mentioned "failure to thrive." These were scary words to Nixon, then a new mom.

If, like Nixon, your baby or toddler falls in an extremely high or low percentile, what does this mean?

Pediatricians monitor growth with charts of height, weight and head circumference. Both the percentiles and rate of growth in these areas are important, says Dr. Robert Riikola, a physician liaison at Le Bonheur Children's Medical Center in Memphis, Tenn. "Generally speaking, if the height, weight and head circumference are above the 5th percentile and below the 95th percentile, and if the rate of growth is steady, the infant or child is deemed to be in 'the normal range.' If, however, there is a dramatic rise or drop in the percentiles, or if the infant or child is above the 95th percentile or below the 5th percentile, further evaluation may be indicated."

There are many possible reasons if the numbers deviate from the norm. It could just be a normal variant. "After all, some of us are big, and some of us are small," Dr. Riikola says. "We can be perfectly healthy and normal – just genetically inclined to be of a certain size."

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