Monitoring children's growthBMJ 1995; 311 doi: https://doi.org/10.1136/bmj.311.7005.583 (Published 02 September 1995) Cite this as: BMJ 1995;311:583
New charts will help
Children whose growth is extremely abnormal are easily recognised. The aim of growth monitoring is to identify children with less obvious but treatable growth disturbances,1 2 3 4 such as growth hormone insufficiency, Turner's syndrome, and hypothyroidism.
Cheap, accurate, self calibrating equipment5 such as the Leicester height measurer and better training should ensure that children are measured accurately. Interpreting measurements is more difficult: there is no easy way of separating children with true growth problems from the more numerous “short normal” children. For this, growth charts are essential.
The Tanner-Whitehouse charts, which have been used in Britain for 30 years to assess height, weight, and head circumference, are now out of date. The average height of British children has increased (the so called secular trend). The increase in breast feeding and the “humanising” of formula feeds are responsible for more rapid weight gain in the first few months of life, followed by a deceleration. Thus the typical appearance of a weight chart for an infant born in 1995 is different from that indicated by the Tanner-Whitehouse chart.
New growth charts are now available, based on seven growth surveys between 1978 and 1990.6 They are called the 1990 nine centile United Kingdom charts and should replace the Tanner-Whitehouse charts. As well as describing current growth patterns more precisely, they have some new features. Firstly, they eliminate the “step” at the age of 2, when standing height is substituted for supine length. Secondly, nine centiles are now provided instead of the traditional seven. The lowest centile is the 0.4 line; only one child in 250 will fall below this line, which is a clearcut indicator for referral. Children with heights between the 0.4 line and the second centile may be normal short children of short parents but merit observation. Similarly, in a child whose height is above the 99.6 centile a growth disorder should be considered. Thirdly, the interval between each pair of centile lines is the same--two thirds of a standard deviation.7 This will simplify interpretation of unusual growth patterns.
The centile lines on standard weight charts do not define a “normal” pattern of growth. Rather, they show the distributions of weights of a range of babies at various ages and are said to be cross sectional. Weight at birth and growth in extrauterine life are determined by different factors, so the weight gain of individual babies may deviate from the centile position defined by their weight at birth as they take up their genetically determined growth trajectory.
A common problem for primary care teams is the baby whose weight gain line is crossing the centiles downwards.8 Failure to thrive is suspected, but when no organic diagnosis can be made, inadequate parenting, neglect, or abuse is considered and child protection procedures may be initiated. These concerns are sometimes justified, but the diagnosis of non-organic failure to thrive is difficult9 and errors can have serious consequences.
If crossing centiles can be normal, how do you decide whether a particular pattern is pathological? Conditional reference charts address this question by defining the centile ranking of the rate of weight gain over a period of time.10 Substantial centile shifts turn out to be much commoner than most people imagine. Unfortunately, the extent of centile shift depends on the starting position--the more extreme the initial weight centile the greater the extent of centile shift. The charts that describe this phenomenon are inevitably more difficult to use than conventional growth charts, but the effort will be worth while and may avoid unnecessary interventions.
How do you decide if a child is too fat or too thin? Answer--use the body mass index, obtained by dividing the weight (in kg) by the height (in m) squared. The body mass index rises steeply in infancy, falls during the preschool years, and then rises into adulthood. It must therefore be related to age and yet another set of new charts enables this to be done.11 The role of these charts in clinical practice has yet to be determined. An extreme centile position does not necessarily indicate disease. The age at which the slope of the body mass index curve changes from down to up (the age of “adiposity rebound”) predicts adult fatness--the earlier the rebound the greater the risk of adult obesity. Whether this pattern could be changed by better diet or more exercise in early childhood is a question for long term research.
The 1990 nine centile charts, the conditional reference curves, and the charts of body mass index come from the same dataset of measurements on white children only. The number of non-white children measured in the various samples was small; furthermore, the influence of social class and the extent and rate of the secular trend vary among ethnic groups. Construction of growth charts for them all would be almost impossible. Data are available, however, on racial differences in growth and body build.6
Monitoring growth is easy to do but difficult to do well.12 An investment in the training of primary care staff should improve referral patterns, and paediatricians must ensure that they, and their trainees, can give sound opinions on these referrals.
The new charts are published by the Child Growth Foundation and are obtainable from: Harlow Publishing, Maxwell St, South Shields, NE33 4PU. Tel: 01914554286; fax: 01914270195.