6. Issues regarding the use of condition-specific growth charts

6.1 Limitations of specialized growth charts

The usefulness of specialized growth charts is limited by a number of factors:

	Developed from very small samples
	Data do not reflect racial, ethnic, or geographical diversity
	Old data used to construct the charts
	Difficult to be sure that the data are representative of the population as a whole or come from a well-nourished group of children within that population
	Inconsistent measuring techniques used (in some cases, chart reviews were used to collect data; for other cases, the measurement techniques were not clearly defined)
	Secondary medical conditions which influence growth potential (and which often accompany a primary chromosomal disorder) not considered

The charts based on the growth of children with trisomy 21 provide some examples of these limitations. (Because trisomy 21 is a chromosomal anomaly, growth potential is altered, and the development of reference data based on this alteration is reasonable.) The clinician using the special charts should be aware of limitations:

	The children in the sample were of limited diversity with respect to race, ethnicity and the geographic location of their residence.
	The nutritional status of the children in the sample was not assessed, so it is difficult to ascertain whether or not the data represent a well-nourished group of children or reflect problems with nutritional status.
	The existence of secondary medical conditions affecting growth (congenital heart disease, which affects about 40% of children with trisomy 21, and feeding problems, which are present in up to 80% of children with trisomy 21) was not considered in developing the reference data.