Subjects and methods

PREPUBERTAL GROWTH IN COMMUNITY SETTING

Community height data were collected for 486 children (247 boys, 239 girls) measured in 11 mainstream schools across the Southampton health district. The children had been routinely measured at school entry (mean age 4.91 years) and again three years later (mean age 7.87 years) by school nurses who had received routine training in the technique and relevance of height monitoring. Each school was serviced by a different nurse, some of whom changed during the study period as frequently occurs in practice. Only children without reported health problems were included. Height measurements were converted to height standard deviation scores (HSDS) using the new UK reference data12 and the prepubertal change in height standard deviation score (ΔHSDS) was calculated by subtracting HSDS of the second measurement from HSDS of the first.

PREPUBERTAL GROWTH IN RESEARCH SETTING

The Wessex growth study13 was set up in 1986 to identify and monitor the growth of short children in the community. A total of 140 short healthy children were identified at school entry as being < 3rd centile for height according to Tanner and Whitehouse standards.14 They were matched for age, sex, and school class with children whose heights were between the 10th and 90th centiles. Children were measured every six months by the same auxologist (LDV) and heights recorded to the nearest millimetre. These were converted to HSDS using the new UK reference data.12The HSDS was calculated for 212 children (109 short, 103 controls) who had a height measurement recorded in the first year of school (mean age 6.05 years) and again three years later (mean age 9.00 years).

STATISTICS

The data were analysed using the SPSS statistical package. The Student’s t test and one way analysis of variance were used to compare means, Bartlett’s test to compare SD, and χ² to compare categorical data. Group results are presented as mean (SD).

Results

PREPUBERTAL GROWTH IN THE COMMUNITY

At school entry, the HSDS of the children was −0.12 (1.00) (46th centile), with no sex difference (boys, −0.14 (0.92); girls, −0.10 (1.07); p = 0.639). Seven (1.4%) children met the referral criterion for abnormal stature, four (three girls, one boy) for short stature (< 0.4th centile) and three (two girls, one boy) for tall stature (> 99.6th centile). At second measurement, the HSDS was −0.14 (0.99) (44th centile) and again no sex difference was found (boys, −0.09 (0.92); girls, −0.18 (1.06); p = 0.090). There were no new referrals for abnormal stature and the height of one initially very tall child then lay within normal limits. The height distributions at first and second measurement (fig 1) were approximately normal and corresponded with the new standards.12

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

Height distribution of 486 children measured in the community at age 5 and 8 years.

The HSDS of 96% of the children did not alter by more than 0.67, the equivalent of one centile channel on the new charts, with 11 (one boy, 10 girls) decreasing and nine (five boys, four girls) increasing their height centile by more than this amount. One child’s height data were excluded from further analysis as the height change was so extreme as to suggest that a recording or transcription error had been made.

The ΔHSDS was close to 0 (−0.01 (0.35)) and normally distributed although girls grew more slowly than boys (boys, +0.05 (0.31); girls, −0.07 (0.38); p < 0.001). Two hundred and ninety three (60%) children had been measured by different school nurses on the two occasions. As might be expected, the standard deviation of ΔHSDS was slightly larger, although not significantly different, for two observers than for one (two nurses, 0.36; one nurse, 0.32; p = 0.16) and nine (including the child excluded from analysis) of the 11 children whose HSDS had fallen by more than one centile channel had been measured by different observers (table 1). The correlation between the two height measurements was 0.948 for a single observer and 0.933 for two observers.

PREPUBERTAL GROWTH IN RESEARCH SETTING

The mean growth of both short and control children in the Wessex growth study stayed close to their initial mean height centile lines. Some grew at a slower rate than others but this was independent of both height and sex. For this population of very short and average controls (10th to 90th centiles14), ΔHSDS was a little above 0 (+0.15 (0.25)). However, the mean ΔHSDS for short and control children was similar (short, +0.18; control, +0.12; p = 0.073). A few children (one short, three controls) increased their HSDS more than 0.67 and one short boy fell by the same amount. For control children, the correlation between HSDS at the two measurements was 0.931, equivalent to a correlation of 0.966 for the whole population, rather than that truncated at the 10th and 90th centiles.

COMPARISON OF COMMUNITY AND RESEARCH RESULTS

Table 2 shows the mean, SD, and SE for ΔHSDS of measurements made in a research setting and in the community by both a single and two different school nurses. Equipment, setting, and observer are prone to variability in the community and the variance of the ΔHSDS was less when measurements were made in ideal research conditions than for community measurements. However, the number of children whose HSDS changed by more than 0.67 was not significantly different (table1).

Discussion

Our data confirm that the 1990 growth reference charts are appropriate for school children today15 and can be used effectively with the recommendations to screen for abnormal stature. The mean height of the children measured in our community was close to the 50th centile, the distribution normal, and the number falling above and below ±2 SDs was as expected. Whether the cut off for abnormally short stature should be the 0.4th centile, as recommended, or be raised to the second centile15 is open to debate, but must depend to a large extent on the resources available.

Our data show that 2.3% of children (one boy, 10 girls) measured in the community would have been identified and referred as “slow growing” and a similar number of children (five boys, four girls) have increased their height centile by more than one centile channel. We do not know why so many girls should be identified as “slow growing” and we consider this needs further investigation. It may simply be chance, recording errors, or the effect of the earlier occurrence of puberty in girls, causing some to transiently fall from their centile before the growth spurt. Nine of the slow growing children had been measured by different observers on each occasion highlighting the problem of interobserver error. Differences between observers, apparently using the same technique, have been demonstrated.16 17 Nevertheless, our findings are compatible with the theoretical model that would have predicted that 1–2% of the reference population would fall and the same number increase by the equivalent of more than one centile channel9 18 between 5 and 8 years old. The joint working party recommendations therefore would not result in an excessive number of referrals for abnormal growth rate, even in a community setting.

There are, however, several areas within the guidelines that need clarification. First, the one child measured in a research setting who was identified as slow growing illustrates the importance of not relying on single estimates of growth rate. He had been measured at six monthly intervals since the age of 5 years and the measurements taken at age 6 and 9 years happen to represent his largest and smallest HSDS. Assessing all his prepubertal height measurements showed that his growth rate was similar to all other short and control children.

Second, the proposal for the identification of slow growth is ambiguous. Growth rate requires both change in height andthe time interval between measurements to be considered. While the guidelines stipulate the change in height required, they do not clearly define the time interval. They simply recommend that children are measured at 5 and again between 7 and 9 years of age, an interval of between 2 and 4 years. However, it has been shown that the variability in the change of height increases as the measurement interval increases.18 19 Therefore, if 3% of school age children drop one centile channel in a 3 year period, fewer could be expected do so in a 2 year period and more in 4 years. A child whose height falls one centile channel in 3 years has grown better than a child falling as much in 2 years but worse if the drop was over a 4 year period.

Third, the guidelines do not specify a method for identifying height centile shift. Visual inspection of the height chart is clearly subjective and open to error. The new UK reference charts can be used to estimate HSDS as outlined by Cole,18 and ΔHSDS calculated by subtraction. However, this would require further training of primary care workers, an additional calculation, and even more instructions on the already overcrowded reference charts. Ideally data should be computerised and children meeting the referral criteria automatically recalled.

The issue of sensitivity must also be addressed before the introduction of a national screening programme. It is generally considered that growth monitoring is good clinical practice that will lead to the early detection of growth related disorders such as Turner’s syndrome, coeliac disease, and acquired hypothyroidism. Our findings suggest that, given reliable height data and a suitable measurement interval, the criterion for the referral of slow growing school age children may well be specific and identify few normal children, but they tell us nothing about its sensitivity. Unfortunately there is little longitudinal data on growth related disease. It is unknown how many children with untreated disease cross centile bands. Disease specific growth charts are available for Turner’s syndrome20 and these show that tall girls with Turner’s syndrome—those above the 0.4th centile on normal height charts—are unlikely to fall by as much as one centile band between 5 and 8 years of age.21Noonan’s syndrome is also associated with short stature; however, Ranke et al reported that the mean height of prepubertal children with Noonan’s syndrome followed Tanner’s third centile and only transiently decreased owing to delayed puberty.22 It is unlikely therefore that growth monitoring alone would detect significant numbers of prepubertal children with undiagnosed Turner’s or Noonan’s syndrome.

Slow growth rate can be a symptom of endocrine and metabolic disorders. While these may severely compromise growth, they rarely stop it completely. The time taken to fall one centile band clearly depends on rate of growth. A school age child would need to grow at half his or her normal rate for over a year before such a fall could be detected. Further studies are necessary to determine which, if any, disorders are likely to be identified through growth monitoring alone.

Finally, in today’s economic climate the need for cost efficiency and effectiveness is paramount. To be successful, a screening programme must be specific and sensitive, but it should also be simple and relatively cheap to administer. The benefit of preschool growth monitoring has yet to be assessed but, even if growth monitoring is proved worthwhile, we should not minimise the planning, training, and cost involved in a national programme.23 Growth monitoring of all children from the age of 2 to 8 years is clearly a multidisciplinary exercise involving the cooperation and commitment of health visitors, school nurses, growth specialists, and administration personnel.