The infancy-childhood growth spurt.

Early normal human linear growth is unstable and oscillates owing to an increase in growth rate between 6 and 12 months of age. This defines the onset of the infancy-childhood growth spurt (IC spurt). The onset is identical with the onset of the childhood component of the infancy-childhood-puberty growth model. The IC spurt is completed when the infancy component of this model has virtually ceased, at around 3 years of age. Additional observations suggest that its onset represents the age at which growth hormone (GH) begins to regulate growth significantly. The negative impact of late onset of the IC spurt on attained height is illustrated and discussed. A delayed spurt is observed in 30-50% of children with growth-related disorders and of infants living in a poor area of a developing country. The IC spurt is absent in children with GH deficiency who receive no hormonal therapy.