Proportionality changes in the first year of life; the influence of weight for gestational age at birth.

Data on 55 small-for-gestational age (SGA), 56 average-for-gestational age (AGA) and 55 large-for-gestational age (LGA) infants whose growth had been monitored regularly from birth to 12 months are presented. SGA head-chest ratios were high at birth; but by 6 months they were very similar to AGA ratios, with values just below unity. Head-length ratios showed a steady decrement; SGA infants having the highest and LGA infants the lowest values at all ages. Chest-length ratios showed little change up to 6 months, with a steady decrease thereafter. Stem-stature ratios showed a similar pattern; and were confined within a narrow margin from 6 months onwards. These changes seem to be target orientated. We suggest the goal is that proportionality which enables the infant to attain the upright stature; and thus to sit, stand and walk at the appropriate time.