Recognising failure to thrive in early childhood. The maximum weight centile achieved by a child between 4 and 8 weeks of age was found to be a better predictor of the centile at 12 months than the birth weight centile. Children whose weight deviated two or more major centiles below this maximum weight centile for a month or more showed significant anthropometric differences during the second year of life from those who showed no such deviation. It is suggested that this leads to a logical and practical definition of failure to thrive. 