How to keep baby growth charts at home

A percentile is a position, not a grade

The line your baby sits on says where they are among other babies of the same age and sex. It does not say whether that is good. For growth, the AAP says, we hope for consistency.

Which is why a home log is useful and a home verdict is not. Three dated points over a month tell a story. One weight on a Tuesday tells you about Tuesday.

Standard or reference: two charts answering two questions

The distinction almost nobody explains. The WHO Child Growth Standards, built from the Multicentre Growth Reference Study on 8,440 healthy breastfed infants across six countries, are a standard: they describe how children should grow under optimal conditions. The CDC 2000 charts, and the French 2018 charts, are references: they describe how children did grow.

So two charts can disagree about the same baby without either being wrong. They were built to answer different questions.

Which chart your country plots on

The CDC and the AAP recommend the WHO standards from birth to 2 years, then CDC reference charts from 2 years up — partly because the WHO data are longitudinal with frequent early measurements, and partly because the measurement itself changes at 2 from recumbent length to standing height.

In the UK, growth goes into the red book, the personal child health record, and the NHS calls the lines on the chart centile lines rather than percentiles. France built its own national reference in 2018 and prints standard deviations instead of centiles. If you move between systems, the same child reads differently on each page.

How often to weigh

The NHS gives explicit maximums: no more than once a month up to 6 months, no more than once every 2 months from 6 to 12 months, and no more than once every 3 months after the age of 1.

Those are ceilings, not schedules, and there is a reason for them. Weighing often at home manufactures noise — a full nappy, a feed, a different scale — and noise on a chart looks like a trend.

One reassurance worth having early: the AAP notes that birth weight is often not regained until 7 to 14 days after birth, particularly for breastfed newborns. The first fortnight is not a straight line for anyone.

Measuring at home is harder than it looks

Length is the one to be honest about. The AAP asks for two people and a measuring board with a fixed headboard and a movable footboard, accurate to 0.1 cm. A tape measure on a changing mat is not that, and the error is larger than a month of growth.

Head circumference has a technique too: a narrow, non-stretchable tape, placed on the forehead just above the brow ridges and round the back of the head to find the maximum circumference, with hair accessories removed.

Weight is the measurement a parent can genuinely take, provided it is the same scale each time and the baby is undressed. Everything else is better left to the appointment.

Corrected age has exact rules

The Royal College of Paediatrics and Child Health is precise about this: never correct for babies born after 36 weeks and 6 days — they are all considered term. Correct until 1 year for infants born at 32 to 36 weeks, and until 2 years for those born before 32 weeks.

The RCPCH also warns that most preterm babies show slow initial weight gain or weight loss, so they appear to fall on the chart early on. Appearing to fall and falling are not the same thing, and telling them apart is the clinician's job, not the app's.

Plotting a point in Wibou

You record weight, length or head circumference with its date, and the point joins the same timeline as the feeds, the nights and the nappies. Not one table in Notes, another in a health app, a third on a folded receipt.

If a reading looks wild, measure again before deleting it. Scales lie once. Two readings in a row that agree are worth keeping.

What a chart at home does not do

It does not tell you whether growth is fine. Every authority treats plotting as an input to an interpretation a clinician makes, alongside earlier measurements and the family's own build. You record the number; your clinician reads it. If something worries you, bring the series — dated points beat a remembered figure every time.