Issues in final height prediction

The desire to make predictions about the future is perhaps inherent in human nature, and methods to predict the final stature of children have existed since the early stages of the development of paediatric endocrinology. Whenever a child with a potential growth problem is brought to the physician. it is a reasonably straightforward procedure to determine the height of the child, and how the child’s height relates to that of a control group of children. However, one of the expressed or implied desires of both the family and the physician is also to determine what the final height of the child will be. and how that will relate to the peer group. As is frequently true, there is a disparity between what the family wants, what the physician wants, and what is available. What the family wants from the physician is, of course, an accurate prediction of final height for their child. What the physician wants from a method of height prediction is a well-validated and accurate method for individual children that can be trusted for use with children who have abnormal growth, not just for those who are growing normally. What is available from the generally used height prediction methods are predictions, with fairly broad error limits, that are based on groups of normal children followed to adult height. The underlying problem in predicting final height is that there is considerable individual variation in the timing and tempo of puberty and in the pubertal growth spurt. Normal children may shift their position on growth curves during infancy ( I . 2). but during the childhood phase of growth, they almost always follow their established channel on growth charts. However, because of marked individual differences in the timing and pace of the pubertal phase of growth, the final height of a child can deviate by as much as 15 cm approximately 2 SD scores (SDS) from that expected from their growth percentile prior to the onset of puberty. Thus, several methods have been developed to predict the differences in the onset of the growth spurt, and are able to improve the accuracy of predicting adult height for individual children. There is no doubt that the most commonly used methods for predicting differences in the onset of puberty, and therefore improving final height predictions, are those involving bone ages. Children’s bones are largely cartilaginous at birth and undergo a predictable sequence of changes in size and shape, ossification and, finally, closure of the cartilaginous epiphyses during the first two decades of life. These changes can be visualized by radiography and compared with control populations to determine an index of bone maturity. The underlying assumption of these methods is that the children who have early maturation of their bones will also enter puberty early, and this allows the effects of the variable timing and tempo of puberty on the final height of an individual to be calculated. This assumption has been validated for groups of normal children by several studies. The bone age and height prediction methods commonly in use are those of Bayley-Pinneau (3). Roche et al. (4) and Tanner-Whitehouse (5). In all of these methods, radiographs of the hand and wrist are used to assess skeletal maturity in comparison with standard data. These control studies are all based on population data from normal children followed to adult height. Unfortunately, the clinician is most often interested in the prediction of final height of a patient with abnormal growth, and there is evidence that there can be systematic errors in the prediction of final height of children with unusual stature (6-8). All these studies were also carried out in populations of limited ethnic variability, so may not be applicable to patients of other origins. In addition, the studies were carried out decades ago, so that any secular trend in development that might have occurred could further confound the results. Finally, there are problems with the reproducibility of the interpretation of bone age films, which introduce another source of error into final height estimation. The net result is that these methods have 95% confidence intervals of 7-9 cm when used to predict the final height of individuals (9). This confidence interval is approximately half that of projecting the final height on the basis of the height percentile before the onset of puberty, and as such represents a clear improvement in accuracy. However, both parents and physicians would prefer a more definitive method for predicting adult stature, or at least one that did not involve a radiograph. There have been several approaches to the development of alternative methods of final height estimation without using bone maturity indices. These include using puberty staging (Tanner scores) (10). the onset of the pubertal growth spurt, and parental height ( I I ) to compensate for the individual variation of pubertal onset and tempo. An entirely different approach has been the use of group data