Reading a growth chart without panicking

Growth charts are one of the few genuinely predictive tools in pediatrics, and they are also one of the most misread documents parents ever take home. The most common thing we hear is a version of: she dropped from the 50th to the 25th, is something wrong?

Usually, no. Here is how we actually read the thing.

Which chart, and why it matters

For children under 24 months we use the World Health Organization charts, which describe how healthy breastfed infants grow. From 24 months we switch to the CDC charts, which run to age 20. This is why a growth chart sometimes appears to jump at the two-year visit: the reference changed, and so did the measurement, because we start measuring height standing up instead of length lying down. A standing height typically reads about half an inch shorter than a recumbent length on the same child.

A percentile is a comparison, not a grade

The 25th percentile means that out of 100 children of the same age and sex, roughly 25 would be smaller and 75 larger. It is not a score. A child who tracks steadily along the 10th percentile with parents who are both short is growing perfectly. A child who tracks along the 90th and suddenly flattens is the one who needs attention, even though they are still bigger than most of their class.

What we watch is the shape of the line over time, not where it sits.

Crossing lines: when it is normal

• Between birth and about 18 months, many babies shift up or down as they move from their birth size, which reflects the uterine environment, onto their genetic curve.
• Around 12 to 18 months almost every toddler's appetite falls off a cliff. Growth rate slows sharply after the first year and toddlers are supposed to eat less than they did as babies. This is the single most common reason parents worry about weight.
• In adolescence, the curve can look wild for two years because the growth spurt happens at different times for different children.

Crossing lines: when we look harder

• A drop of two major percentile lines in weight, or any drop in the height curve
• Weight falling while height keeps climbing, which points at intake or absorption
• Height falling while weight holds, which points at an endocrine or systemic cause
• Head circumference crossing lines in either direction in the first year
• No growth at all over six months in a child who should be growing

BMI in children is not adult BMI

From age two we plot BMI, but a child's BMI number on its own is meaningless. It has to be read as a percentile for age and sex, because body composition changes enormously through childhood. BMI normally falls to its lowest point around age five or six and then rises again, which is called adiposity rebound. A rebound that happens early can be worth a conversation.

We will always show you the curve on screen and talk about what it means. If you ever leave a visit unsure, send a portal message and ask. There is no such thing as an annoying question about your own child's growth chart.

If this is a medical emergency, or your child is struggling to breathe, unresponsive, having a seizure, or badly injured, call 911 now. Call 911.

General information, not medical advice. It is not tailored to your child and it does not replace a visit. Guidance changes. This article was last reviewed on the date shown above.