The decanalization of weight, recumbent length, and head circumference during infancy

This study has estimated the extent to which 659 infants in the Fels Longitudinal Study maintained their positions in canals on the current NCHS growth charts during 6- and 12-month intervals. These canals are the zones between adjacent major percentile lines (5th, 10th, 25th, 50th, 75th, 90th, and 95th) on the growth charts. The probabilities of increases or decreases in level by two or more canals were calculated. Additionally, the probabilities were calculated for changes in level from between the 5th and 10th percentiles or between the 90th and 95th percentiles to zones beyond the 5th or 95th percentiles, respectively (transitions from normal limits). The analyses were made from birth to 36 months for weight and from 1-36 months for length and head circumference. The probabilities of decanalization were larger for weight than for length or head circumference for the interval from birth to 6 months, but not later. The probabilities for each variable analyzed tended to be large for young age intervals and larger for changes toward the medians than for changes from the medians. The directions of decanalization for weight from birth to 6 months were related to birth weight and those for length were related to midparent stature for the intervals from 6-12 months in each sex, 1-12 months in girls, and 6-18 months in boys. Am. J. Hum. Biol. 9:689-698, 1997. © 1997 Wiley-Liss, Inc.