Growth Charts Explained and in Perspective

By Megan Reynolds

Weight gain in infants is an objective measure which is often heavily relied upon when assessing children’s health. When your child is gaining “good weight” you are assured that you are feeding them well and they are healthy. When your infant is not gaining “good weight” you question your parenting skills and start worrying about whether your child is healthy or not. However, there is more to your infant’s health than weight gain and its significance should be placed into perspective.

Normal infant weight gain

La Leche League report that your baby should gain at least 4-7 ounces per week after the fourth day of life, that is, 113g – 198g per week after the fourth day.

Growth charts in NZ

In July 2010 the Ministry of Health introduced a series of new growth charts. They are based on growth standards developed by the World Health Organisation and the Royal College of Paediatrics and Child Health, UK. These charts set breastfeeding as the norm and describe optimal rather than average growth. It is argued that breastfed babies show similar growth rates globally and bottle fed infants should, at least, keep up with breastfed infants’ weight.

Data was collected from birth to age five in six countries (USA, Norway, India, Ghana, Brazil, Oman). Infants were only included if they were healthy and born at term, were breastfed exclusively for at least four months, with continued partial breastfeeding for a year and complementary foods started by six months. Mothers were non-smoking and lived in comfortable economic circumstances.

Key changes in the 2010 growth charts

The data on which the charts are based have changed but there are also some key formatting changes:

  • There are no centile lines for the first two weeks. This is because of the great variation in weight gain (or loss) at this early age. Percentage weight loss is considered more important at this stage with a loss of more than 10% suggesting that further assessment is recommended.
  • The centile lines have been extended from the old 3rd – 97th to 0.4th – 99.6th. This change effectively broadens the boundaries for the normal range and ensures that those beyond them are truly outside the normal range.
  • The 50th centile line is no longer bold. This is an attempt to lessen parents concern that this is where the normal lies. “Normal” is anything within the limits (0.4th – 99.6th).

As an example of how the charts have changed: my son was charted well below the 3rd centile at 17 months (not on the graph) when if charted on the new graph he would have been within the 2nd centile well within the chart. His weight was in proportion to his curve and taken in context at the time – but there is something reassuring about being within the graph.

How to use the charts

The charts are designed to assess your infant’s growth rate over time – to ensure that they are following a similar pattern to the norm. It is not an exam where 99.6 is the goal, any placement within the outer boundaries is considered normal. If your child is in the 2nd centile it means that in a group of 100 average infants 1 child would weigh less and 98 would weigh more than them. Half of all infants lie between the 25th and 50th centiles. The one off placement of your infant on the graph is unimportant, it is how they track over time which is the key to using the charts correctly.

How often should you weigh your baby? Once you are discharged by your midwife baby is usually weighed at the time of routine check-ups – around 2, 3, 4 and 13 months of age. Weighing may be more frequent if there is concern for your infant’s development or health. However, it is not recommended that infants be weighed too frequently as daily fluctuations become more significant (if you weigh your infant after a big feed/or before). At most, babies should be weighed once a month from 2 weeks to 6 months of age, every 2 months up to 1 year of age, every 3 months after that.

It is normal for the plotted weights to ‘wiggle’ up and down a bit, or to move gradually from being near one centile to the next one (up or down). It is less common for a child’s weight to cross two centile lines and assessment from your primary health practitioner should be considered. Even when your infant has lost weight due to an acute illness they should bounce back to their centile within 2-3 weeks.

It is important to be accurate when plotting your infant’s weight. The most common error is in calculating the age and this can alter your infant’s curve significantly.

Your baby’s weight in perspective

If your baby is not gaining weight according to the norm, there are other things to consider:

Is your baby peeing and pooing well?

Is your baby’s urine either clear or very pale yellow?

Are your baby’s eyes bright and alert?

Is your baby’s skin a healthy colour and texture?

Is your baby moving its arms and legs vigorously?

Are baby’s nails growing?

Is your baby meeting developmental milestones?

Is your baby’s overall disposition happy and playful?

When your baby is awake does he have periods of being very alert?

Is your baby eager to breastfeed?

If you answered yes to all of the above, it is most likely that your infant is developing just fine. Don’t lose faith in your breastfeeding based just on their weight. Infants, like adults, come in all shapes and sizes.

Trust your instincts

Although weight can be an indicator of health it is only one component and serious illness will present with more than just a weight change. You know your baby best and instinctively know whether they are happy and healthy or unwell. I always find it amusing when my GP comments on how happy and well my children look (prior to examination as if to say your kids can’t be sick!) only to find a high fever and raging ear infection, terrible constipation… If you are concerned about your baby’s health talk to your health care provider.

References and Articles of interest

UK_WHO Growth Charts – Understanding growth charts: what they tell you about your child’s growth from Royal College of Paediatrics and Child Health, UK.

Child Health in New Zealand – Growth Charts information sheets from Ministry of Health.

How can I tell if my baby is getting enough milk? from La Leche League.

Look at the baby, not the scale from Jay Gordon, MD FAAP.

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