Understanding your baby's centile chart

The Red Book

We’ve all been given one by our midwife or health visitor shortly after the birth of our bundle of joy. This is your Personal Child Health Record and amongst its pages, you will find your baby’s growth charts.

Sometimes called percentile charts or simply centile charts, these charts are how your baby’s growth is assessed and sometimes how health issues are identified.

How your baby grows in the first year of life terms of her weight, length and head circumference is linked to her future health. This is why each baby born in the UK is issued with their ‘red book’ and why your Health Visitor likes you to pop along to the child health clinic to have her weighed at regular intervals.

Personal Child Health Record

Personal Child Health Record

What are the growth charts describing?

The centile charts are published by the Royal College of Paediatrics & Child Health RCPCH and were created by measuring thousands of babies born between 1997 and 2003 from 6 different countries who were born at full term, who were healthy and who had mummy’s who didn’t smoke and enjoyed a healthy pregnancy. The babies were all predominantly breastfed for the first 4 months of life and were introduced to weaning foods by 6 months with continued breast milk throughout their first year.  The researchers producing the centile charts were aiming to capture what optimal growth looks like.

Therefore the growth charts in your red book describe how a baby should grow in pursuit of good health and are there to be used by parents and health care professionals together to assess whether your baby is thriving in the way we would expect.

What are the curved lines and what do they mean?

The lines on the growth chart are called centiles (or percentiles) and show the expected pattern of growth. The numbers refer to the percentage of babies at or lower than the line, for example, a baby whose weight is on the 50th centile means that 50% of babies the same age as her are the same weight or less. 

The centile line curves range from 0.4th centile to 99.6th centile which indicate the normal growth range. However this also means that there will be 4 babies in every 1000 who are less than the 0.4th centile and 4 babies in every 1000 who are greater than the 99.6th centile who are also considered normal.

There are separate charts for girls and boys as the way they grow is different. There are also unique charts for premature babies and charts for babies with certain genetic conditions.

Why it’s important to weigh and measure your baby regularly

Your baby grows rapidly during their first two years of life, in fact they grow fastest now than at any other time. By 6 months most babies will have doubled their birthweight and grown about 12cm in length, and by the time they are two years old they will be roughly half their adult height. Head circumference increases too due to rapid brain growth.

The rate of growth is predominantly influenced by your baby’s nutritional intake which is why it’s so important to get it right from the start of weaning, when neither breastmilk or formula alone can provide the necessary nutrition for your baby. If you’d like to learn more about Baby Nutrition you’re welcome to join my digital course.

What normal growth looks like?

Your baby’s growth should follow a centile curve consistently throughout their first year. They don’t need to be on an actual line, they can be between them, so long as their growth roughly follows the shape of the curve.  Fluctuations are normal and the key is to look at your baby’s changes in weight, length and head circumference over time. They don’t have to be on the same centile number for both weight and height, that’s what makes us all unique. Some of us are tall and thin, others shorter and heavier. Nevertheless, the majority of babies should track the same pattern throughout their first year and throughout childhood.

Gaining too much weight

Sometimes a babies weight goes up too rapidly and moves upwards across the centile lines. Research tells us that this is sometimes a result of overfeeding - usually milk feeds. Rapid weight gain during the first year of life is associated with increased risk of obesity later in life and may be a predictor of heart health although studies so far have been inconclusive. If you want to understand how much milk your baby should be having once they've started weaning you can check my portion size guide.

Sometimes babies who gain weight rapidly also gain height velocity too and grow up to be taller individuals.  Unusual weight and height gain can sometimes be an indicator of an underlying problem, so if you notice this talk to your health visitor or other health professionals, it may be that a referral to a dietitian is warranted to assess how much he or she is eating and drinking or a referral to a paediatrician is needed for further investigation. 

Not gaining enough weight

Conversely a sudden weight loss and centile drop can occur following a period of illness, which usually recovers within 2-3 weeks, however, if the drop continues through two or more centile lines talk to your health visitor or GP, it may be that your baby needs some extra help to regain his weight.

When babies start to regain weight after a period of faltering growth (or if they were born small for their age and are exhibiting ‘catch-up’ growth) care must be taken to ensure that weight gain is not too rapid. This too is linked with having an altered body composition and higher fat mass in both childhood and as an adult, which has its own health consequences. A Registered Dietitian can support you through this process.

Centile chart

Centile chart

How to weigh and measure your baby accurately

Babies should be weighed in no clothing if possible; even a clean nappy can make a difference to where they fall on their centile chart. Only use the scales that your health visitor provides as these are calibrated for accuracy.

For the first year, your baby’s length is measured lying down. Again with no clothing, shoes or nappy. Specialist measuring equipment is required; your health visitor may have a special mat or board. Two people are needed to ensure an accurate height measurement is taken and it’s important one of these is a health care professional.

After 1 year of age, standing-height is measured instead. It’s not unusual for baby clinics do not routinely offer length measurements, it takes two people and NHS resources are stretched. Many clinics are run by support workers rather than Health Visitors and some even encourage parents to self-weigh their babies. My local clinic did. You may need to request an appointment if you want your baby’s length to be measured.

Your baby should be weighted a week or so after birth, then at 6-8 weeks, 12 weeks and 16 weeks. A lot of parents are tempted to weigh their babies more frequently than this but it's important not to do so more than once a month up till 6 months of age then once every 2 months between 6 and 12 months of age. This is because natural fluctuations take place and can be misleading and worrying for both parents and health care professionals.

When your baby is weighed for the first time in a week or so after birth, there are no centile lines on the growth chart to plat them against. This is because weight fluctuates a lot from baby to baby during the first two weeks of life, so there is no expected standard. The vast majority of babies will be around the same weight as their birth weight at 2 weeks, often babies lose weight during this period and then regain it. Being the same weight or more at 2 weeks of age is an indication that feeding is going well and that your baby is healthy.

What age does the centile chart go up to?

The growth charts in your red book go up to 20 years of age for boys and 18 for girls as this is when growth stops for the vast majority of young people. There is an adult height predictor which can be calculated to determine your childs adult height potential too, ask your health professional to do this for you!

From 2 years of age, you can continue to weigh and measure your child at home and record their measurements on the pages given, there's no need to take them along to the baby clinic although do take your child's red book with you when you have appointments with other health services.

Further information:

If you’ve found this post useful and want to know more about your baby’s nutrition and growth during their first year of life, I host a digital course called ‘Baby Nutrition, Weaning and Getting Feeding Right’ and I’d love to have you join me.

Sarah Almond Bushell MPhil, BSc (Hons) RD MBDA - Registered Dietitian & Children’s Nutritionist

Sarah Almond Bushell MPhil, BSc (Hons) RD MBDA - Registered Dietitian & Children’s Nutritionist