The term catch-up growth refers to the acceleration seen in many children during recovery from serious illnesses or from environments that retard growth. Two conditions are necessary for this designation
- i) Growth retardation as shown by previous low percentile levels of measures and
- ii) Subsequent increase in these percentile levels.
It has been well documented that whenever a child suffers for a short period of time from an illness or starvation he/she is able to return to his regular course of growth, when conditions improve due to proper treatment given for the respective problem. In doing so his initial growth velocity after recovery is unusually large (higher than normal) than expected of children of his age. Such a higher than normal velocity has been named ‘catch-up growth’ by Prader, Tanner and Von Harnack in 1963. For example, if there are three children suffering from different problems, first child from malnutrition, second from hypothyrodism and third from cortisol producing tumour (growth-inhibiting), all three will show growth retardation. However, when all three children get completely treated for the respective conditions, then during recovery catch-up growth will occur in all of them. The velocity during the initial period of catch up may reach three times the normal for age, where after, it slows down to its normal velocity. The power to stabilize and return to a predetermined growth curve after being pushed off the trajectory is called by Waddington ‘canalization’ or homeorhesis (homeostasis being the maintenance of a static condition and homeorhesis being the maintenance of a flowing or developing one). The effect of unfavourable conditions on growth seems to depend upon the duration and the severity of the insult and age at which it occurs. Catch-up growth may completely restore the situation to normal or it may be insufficient to do so. In less favourable circumstances where treatment is incomplete or less effective, the child may resume growth at a normal, but not higher than normal velocity. The result of this may still be satisfactory, since if skeletal maturation is delayed, as is usual in such circumstances, the growing period will be extended and thus the final height will be close to normal, though reached late.