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...
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).