During the first year of life, an infant's weight and length are charted at each doctor's visit to make sure that growth is proceeding at a steady rate. Percentiles are a way of comparing infants of the same age. For an infant at the 10th percentile for weight, 10% of infants weigh less and 90% weigh more. For an infant at the 90th percentile, 90% of infants weigh less and 10% weigh more. For an infant at the 50th percentile, 50% of infants weigh less and 50% weigh more. Of more significance than the actual percentile is any significant change in percentile between doctor's visits. (Adapted from WHO Child Growth Standards. Available at www.cdc.gov/growthcharts.)