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Assessing Growth and Body Mass Index on Centile Charts 41
Head circumference is usually measured within The 2nd and 98th centiles are two standard
24 hours of birth and at the 6–8-week check; deviations (or two z scores) above and below the
thereafter only if there are neurodevelopmental median.
concerns.
In the UK, two sources of data for construction
Clothing of the recommended reference charts are used
(Table 2.1.4):
Infants and children up to 2 years should be
weighed naked, without a nappy. Thereafter they ●● The UK 90 reference data is from a large number
can be weighed in underwear or very light clothing of measurements of children living in the UK
without shoes or socks. during the 1980s and up to 1990. These charts
describe the average growth of children at this
Supine (lying on the back) length is measured up time before the epidemic of childhood obesity
until 2 years and without clothing or a nappy as this began. They are considered a reference for
can distort the hips and make the measurement normal growth in the UK.
inaccurate. Standing height is measured after
2 years of age and children can wear clothing but ●● The World Health Organization data WHO
should remove shoes and socks. Any head wear Child Growth Standards were developed using
such as topknots must also be removed. data collected in the WHO Multicentre Growth
Reference Study, which was a community-based,
Measuring equipment multi-country project conducted in Brazil,
Ghana, India, Norway, Oman and the United
Only class III clinical electronic scales in metric States. In each of the six countries a sample of
setting should be used to weigh children. These breastfed infants from non-smoking,
should be maintained and calibrated annually, in non-deprived mothers were measured
line with medical devices standards EC Directive longitudinally. Growth was found to be similar
90/384 EEC. in all six countries and growth charts using the
data describe the optimal growth 0–4 years for
Most equipment for measuring length and all children from different ethnic groups.
height is self-calibrating or should be adjusted with
a standard measure. Table 2.1.4 Data sources for different age groups
Tapes for measuring head, waist, hip or limb Age group Source of data
circumferences should be made of a narrow, Preterm infants
non-stretchable material such as paper or plastic. Term infants at birth UK 90 reference data
2 weeks to 4 years of
Growth charts age UK 90 reference data
Growth charts have been constructed by measuring 5–18 years WHO data collected in the
a large number of healthy children at varying ages. WHO Multicentre Growth
Centile lines are then constructed showing the Reference Study
normal distribution of weight/height/head
circumference measurements at each age. The 50th UK 90 reference data
centile line is the median of the measurements for
that age. Fifty per cent of children will have Growth charts recommended for use
measurements below that line and the other 50 per
cent will be above that line. The other centile lines in the UK
are constructed using standard deviations from the
median. The 25th and 75th centile lines are 2/3 The growth charts in the UK have nine centile
standard deviation from the median. Twenty-five lines: 0.4th, 2nd, 9th, 25th, 50th, 75th, 91st, 98th
per cent of children’s measurements will be below and 99.6th (Table 2.1.5). Each type comes in one
the 25th centile line and 75 per cent of children’s version for boys and one for girls as boys and girls
measurements will be above that centile line. have slightly different growth patterns. The correct
term for the area between the centile lines is ‘centile
space’.
