Growth and its Measurement

Gives healthcare professionals (HCPs) information on how to measure, plot and interpret growth in infants and toddlers. Measuring the weight and height of children is a useful non-invasive method of assessing their wellbeing. You can detect deviations in growth from the norm: for example faltering growth, in terms of length/height or weight gain for instance, and the early signs of obesity, shown by an increased BMI.

Growth charts are a visual representation of the normal distribution of the heights and weights of healthy children. By plotting and comparing an individual child’s measurements over time, you can determine whether the child is following an expected growth pattern, which can be very reassuring to parents. Three charts are used most commonly: one for weight, one for length/height and one for head circumference. There are separate growth charts for boys and girls as growth rates differ slightly between genders.

Of these, weight is most often used by parents and HCPs alike, as the measure of growth in infancy.

When assessing the growth of a toddler both weight and length/height should be measured. A single measurement of weight and height does not show if a child is growing normally or if there are any growth problems. Measurements of weight and length/height at intervals of about three and six months respectively are needed to provide meaningful information about growth rate.

How to plot

• First, work out the age of the child, remembering to adjust for infants born preterm. An age wheel can help
• Plot age on the horizontal axis and measurement value on the vertical axis
• Use a pencil dot to mark the chart with the measurement. A straight edge, such as a ruler, can help to locate the intersecting point of the axes
• Do not use a cross or a dot with a circle around it, as it becomes difficult to read these symbols when they are plotted closely together.

After plotting a set of measurements, check to see if they are consistent with earlier measurements (that they are on roughly the same centile lines as before). If not, check the measurements, plotting or calibration of scales.

When you have made accurate measurements, calculated age correctly and plotted them on the appropriate growth chart:

• Use the information for clinical assessment
• Share the information with the family (i.e. translate into an explanation that is useful to them).
   

When to weigh: equipment and calibration

Birth weight should always be recorded and plotted according to gestational age. Attendances for routine immunisations and health checks offer opportunities to measure an infant’s weight. NICE also recommend weighing at five and ten days.

There is no value in measuring weight too frequently; the smaller the time interval between measurement the larger the apparent fluctuations in weight. A feed can add 200g to an infant’s weight. For children over one year it is rarely useful to measure weight more than once every three months. Below this age, children should be weighed at no more than one monthly intervals.

NICE¹ and Hall and Elliman² recommend that normal healthy babies should be weighed, as a minimum, at birth, and in the first week, as part of an overall assessment of feeding and thereafter as necessary until birth weight is recovered – usually at about five and ten days. Thereafter, healthy infants should usually be weighed, at the time of routine immunisations which is at 8, 12 and 16 weeks and at 1 year. If there is concern, weigh more often, but no more than once a month up to 6 months of age, once every 2 months from 6–12 months of age and once every 3 months over the age of 1 year. Children will be weighed at their 2 year check and then on entry to primary school.

There are now European legislation and regulations for the use of digital electronic scales and these should be adhered to. Measurements should be made in kilograms (kg) and grams (g). Infant scales can be used for toddlers of up to 10kg. Toddlers over 10kg should be weighed on sitting or standing scales as appropriate.

The regular calibration of scales is very important in order to ensure accurate measurements.

Scales should be calibrated regularly and checked annually. The companies that sell scales all offer service agreements to do this. You can check that the scales are working properly by weighing a known weight. Equipment companies sell these, but you could use something like a packet of pasta of known weight. It is very important to check portable scales each time they are moved.

In hospital, a daily check should be done using a known weight. The annual calibration should be carried out by the medical physics department or by an outside contractor.

It is the responsibility of the person using the scales to make sure they are maintained and calibrated. If many people use them, such as in the community, one person should be responsible for this.

When to measure length/height: equipment and calibration

There is no evidence to support the routine measurement of length in the first two years of life. However a routine length/height measurement is recommended for all children who are born preterm, are small-for-gestational age or have any dysmorphic features. Up until a toddler’s second birthday, length is measured lying down and after that standing height should be measured (as long as the child can stand appropriately). Children’s height will be measured at their 2 year check and whenever you have an opportunity to weigh children over two years old, use it as an opportunity to measure height as well.

Calibration for length/height equipment is equally important. Some equipment is self-calibrating or a standard measure can be purchased and used. A Leicester Height Measure, a stadiometer with the scale fixed to the footplate, is the ideal equipment because when installed correctly, it is self-calibrating. A stadiometer fixed to the wall must be installed appropriately to be accurate and should always be calibrated with a 60 cm rule before use. For children under two years old, either a rollameter or a lying stadiometer should be used.

Note: if the parents come to you with heights and weights in feet, inches, ounces and pounds (imperial system), you can convert to the metric system using conversion charts or downloadable programmes (hyperlink to weight conversion tool).
 

When to measure head circumference

This should be measured at birth and at six to eight weeks. Immediately following birth the head of a new born baby can be misshapen so this measurement is normally taken at approximately 24 to 30 hours after birth. If there is a crossing of centile upward or downward or signs compatible with hydrocephalus or microcephaly then two further measurements over a four-week period should be carried out. Obviously if there are concerns about a child’s development then measuring the head circumference should be part of a full normal neurological examination.

How to measure head circumference

The recommended tapes are plastic tapes which need to be threaded. They are made from a thin plastic that will not stretch and lead to inaccurate measurements.

Always measure the head circumference three times, to the nearest millimetre, and take the average measurement. You place the tape around the middle of the forehead making sure to use the widest diameter between the frontal and occipital bones.

Assessing head circumference

Rapid increases in head circumference are most commonly seen in the first year, before the anterior fontanelle closes. Failure of the head to grow is usually accompanied by evidence of developing neurological abnormalities and should, with details of the child’s developmental progress, prompt referral.
 

How to weigh

Up until their second birthday, toddlers should be weighed nude, without a nappy. Over this age they should be weighed in light underwear without shoes and socks. If children over two who are still wearing nappies, they should have their nappy removed before being weighed. Alternatively you can subtract the weight of the nappy from the child’s weight measurement.

Children under two years of age should be weighed to the nearest 10g (1/100th of a kg). Over two, toddlers should be weighed to the nearest 100g (1/10th of a kg).

A calm atmosphere is very important and often difficult to achieve in a busy clinic or surgery. Use distractions such as bubbles to occupy children. As a last resort they can be weighed with their parent on a floor scale. You can do this either by subtracting the parent’s weight or by re-zeroing the scales with only the parent on the scales before they hold their child.

Assessing weight

In the first two years of life poor weight gain raises most concerns. There are no universally agreed definitions of ‘faltering growth’ or ‘failure to thrive’.

Interpretation of weight should start with a check of the current measurement, a review of previous weight measurements, the social and domestic environment of the child, and most importantly a review of his or her nutritional intake.

Each primary care clinic may have its own routine for managing the children whose weight appears to be increasing or decreasing faster than expected.

An indication of possible weight faltering is a fall across two centile spaces (more information can be found in the ‘Growth’ Module). If a child has been following close to the 50th centile and then drops to the 9th this may warrant concern.

The majority of infants with faltering growth do not require referral to a paediatrician. In most cases the cause becomes clear with investigation of their social background, feeding history and history of minor illness. Only a minority of those referred will have an organic cause.

Using Thrive Lines to monitor an infant’s weight gain

If an infant is weighed every four weeks then thrive lines may be useful in determining how usual or unusual an infant’s growth is. Thrive lines are supplied as acetates to overlay the growth charts.

Thrive lines can be useful for the infant whose initial weight is higher than the 50th centile because weight loss in these infants can easily be misinterpreted.

Growth greater than the 95th thrive line for an eight-week period can be used as a screen for excessive weight gain.

When to refer

There is no nationally agreed referral pathway for infants whose weight gain or loss is thought to be excessive.

Refer

• Any child about whom you have clinical concern to the GP or in the case of a school age child, discuss with the community paediatrician (if one is available) or the GP
• Any child whose growth appears to be continuing to climb or fall through the centiles after three measurements have been taken at monthly intervals in the first year, or three monthly intervals in the second year
• Any child with a weight below the 0.4th centile unless they have been small from birth
• Any child whose weight falls across two centile bands
• Any infant whose weight centile is more than two centile lines above that of the length/height centile OR the weight has crossed centile lines upwards.
   

How to measure length/height

Measuring children with any clothing, including a nappy, can distort the hips and shorten the length. Thus, babies up to 24 months of age should be measured nude. This also gives an opportunity to assess the child’s proportions. Two people are needed to obtain an accurate length measurement – one to support the child’s head against the headboard of the device and one to gently flatten the knees and flex the ankles of the toddler to 90 degrees and bring the footboard up to the flat soles of the flexed feet. The corner of the infant’s eye should be in a horizontal line with the middle of the ear. Measure the length to the nearest 1/2 cm. Readings in a specialised unit by experienced staff may be taken to the nearest millimetre. If the parent is helping, it is best for him or her to hold the child’s head against the headboard.

When children reach 24 months of age you can measure their standing height. The child should stand as straight as possible with his or her heels, buttocks and shoulders touching the measuring device, looking straight ahead. The Frankfort Plane – an imaginary line between the middle ear and the upper border of the lower orbit of the eye – should be parallel to the ground.

Maximise height by lifting the head slightly by putting fingers under the jaw line just below the ears (known as the mastoid process), and measure to the nearest millimetre.

Measuring length is more difficult because children do not like lying down or being held in the appropriate position. Common difficulties include them pointing their toes and getting their ankles to 90 degrees.

If you are concerned by a child’s length/height then you should use the Parent Height Comparator on the 2-18 years Growth chart. Plot the heights of both parents on the mother’s and father’s height scales in the Parent Height Comparator box and join the two points with a line. The mid parental centile is where this line crosses the centile line in the middle. Compare this to the child’s current height centile. Nine out of ten children’s height centiles are within +/- two centile spaces of the mid-parental centile.

Assessing height

Any preterm, dysmorphic or small-for-gestational age babies should have had his/her length measured at birth. After that time it is recommended that children only have their height measured if there is a concern. A referral should be made if the length is greater than the 99.6th centile or lower than 0.4th centile. An endocrine abnormality is more likely if the child is short and fat as opposed to short and thin.

If there have been serial measurements of length/height then a change of one centile space over one year up to the age of five years may warrant referral.

At present there is only one evidence-based national guideline regarding measuring children and that is to measure the height of all children at school entry. The 0.4 centiles should be used as a cut-off for referral. This should identify at least half of all previously missed children with growth hormone deficiency and girls with Turner syndrome. It is suggested that this would pick up 40 cases of Turner syndrome and 80 of growth hormone deficiency per year³.

When to refer

• Any child with a single length or height measurement below the 0.4th centile for investigation of ‘short stature’
• Consider every child above the 99.6th centile for referral along with the weight
• Any infant whose length centiles are over two centile spaces apart
• Any child over one year whose height has crossed one centile space up to five years of age
• Any infant whose length/height centile is more than two centile lines below that of the weight
• Any child whose height centile is significantly outside the child’s expected centile range following a calculation of the mid parental height centile
• Any child whose parents express particular concerns about their height.
   

The Personal Child Health Record (PCHR) which contains all the standard growth charts from birth to 18 years, and is given to every family on the birth of a new child, should be the prime record of the child’s growth. There are separate charts for both boys and girls. The PCHR is held by parents and so they should have the charts to hand to be filled in when necessary. They can offer reassurance when their child is developing normally but can also highlight any concern in their child’s growth.

You may need to explain to parents what the various plots on a growth chart mean when plotting a child’s growth. It is helpful for parents to understand how growth charts work so that they can follow their own child’s development. You can use the plotted chart to offer reassurance and use it to explain any causes for concern.
 

A calm atmosphere is very important when weighing a child, to prevent them from becoming too distressed and crying. Distraction techniques including blowing bubbles and playing with toys are good examples.

If in some cases this doesn’t work, the child can be weighed with their parent, then the parent’s weight subtracted – either by zeroing the scales or by subtracting the parent’s weight.

In order to get a child’s feet at a 90-degree angle when measuring their length, try stroking or tickling their feet.
 

Measuring growth in preterm infants is done in exactly the same way as measuring the term infant. It is important to distinguish between their gestational age, their actual age from birth and their corrected age and to plot appropriately on a growth chart.

For infants born before 37 weeks gestation their birth weight and any weights up until the equivalent of 42 weeks gestation should be plotted in the box specifically for preterm infants.

After this you need to adjust throughout the first year for preterm infants born between 32 and 37 weeks gestation and adjust over two years for preterm infants born before 32 weeks gestation. You can do this by first plotting the measurement at their actual age and then drawing a horizontal line backwards for the number of weeks of prematurity and marking this new measurement with an arrow.

For example a 32-week preterm infant at 12 weeks of age would be plotted first at 12 weeks of age and then a horizontal line drawn backwards from that measurement through 8 weeks so that the corrected age plot is marked by an arrow to four weeks post term.
 

To assess whether a child is overweight or obese, a BMI should be calculated by dividing weight in kg by the square of the child’s height, in meters, and plotting on a BMI chart.

Alternatively you can use an online programme.

There is a BMI chart for boys and one for girls and they can be ordered from Harlow Printing Limited. These charts are used for children from one to 18 years. The normal range of BMI for adults (18.5 – 25) is not applicable to children as BMI changes throughout childhood. (See Factsheet 3.3 for more information on obesity).
 

Thank you to:

• Sheffield Children’s Hospital
• Dr Robert Coombs, Consultant Neonatologist
• Sally Carney, Endocrine Nurse Specialist
• Tanya Urquhart, William and Edward Kelly
• Kerry and Lily Hodgkinson