The WHO infant growth chart is a set of curves showing how healthy children typically grow from birth to age 2. Released by the World Health Organization in 2006, these charts are the recommended standard in the United States and most countries worldwide for tracking weight, length, and head circumference during the first two years of life. If your pediatrician has plotted your baby’s measurements at a well-child visit, they almost certainly used these charts.
What the WHO Charts Actually Measure
The WHO charts track four key metrics for infants from birth to 24 months, with separate charts for boys and girls:
- Weight-for-age: how your baby’s weight compares to other children of the same age and sex
- Length-for-age: how your baby’s length (measured lying down) compares
- Weight-for-length: whether your baby’s weight is proportional to their length, which helps identify if a child is too thin or too heavy for their body size
- Head circumference-for-age: how the size of your baby’s head compares, which reflects brain growth
Each chart displays curved lines representing percentiles: the 2nd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 98th. These lines let you see exactly where your child falls relative to the broader population of healthy infants.
Why WHO Charts Are Used Instead of CDC Charts
You might wonder why there are two sets of growth charts floating around. The CDC created its own charts based on how American children actually grew during a specific time period. Those charts are a growth “reference,” essentially a snapshot of what happened. The WHO charts, by contrast, are a growth “standard.” They describe how children should grow under optimal conditions.
The distinction matters most for babies. The CDC recommends that U.S. clinicians use the WHO charts for all children under 24 months and reserve the CDC charts for ages 2 and older. One major reason: the WHO charts are built around breastfed infants as the norm. Every infant in the WHO reference population was breastfed for at least 12 months and predominantly breastfed for at least four months. Breastfed babies tend to grow differently than formula-fed babies, gaining weight more quickly in the first few months and then more slowly later. Older charts based mostly on formula-fed babies could make a healthy breastfed infant look like they were falling behind, triggering unnecessary concern.
How the Charts Were Created
The WHO charts came from the Multicentre Growth Reference Study, which collected data from children in six countries across different continents. The researchers didn’t just measure any children. They specifically selected families where conditions favored healthy growth: mothers who didn’t smoke, babies born at term from single pregnancies, households with good socioeconomic conditions, and communities where mothers had access to breastfeeding support. Children with significant illness were excluded.
This deliberate selection process is what makes the charts “prescriptive” rather than descriptive. They don’t reflect average growth in a given population (which could include malnourished or overfed children skewing the data). They reflect how children grow when nothing is holding them back. That makes them a more reliable benchmark regardless of where a child lives.
How to Read Percentiles
Percentiles rank your baby against 100 other children of the same age and sex. If your baby’s weight is at the 50th percentile, half of healthy children weigh more and half weigh less. If your baby is at the 90th percentile for length, only 10 out of 100 children are longer. A baby at the 15th percentile for weight is heavier than 15 out of 100 children and lighter than 85.
The most common misunderstanding is that higher percentiles are “better.” They aren’t. A baby consistently tracking along the 20th percentile is growing normally. A baby at the 90th percentile is also growing normally. What matters most is that your child follows their own curve over time, not that they sit on any particular line.
When Percentile Changes Are Normal
Babies don’t always lock onto one percentile line and stay there. During the first two to three years, it’s normal for children to shift up or down by one to two percentile lines, often drifting toward the 50th percentile. A baby born large (say, at the 90th percentile) to average-size parents may gradually settle into a lower percentile that better reflects their genetic potential. Similarly, a smaller newborn may climb upward.
What raises concern is a rapid or dramatic change. A baby who drops from the 75th percentile to the 10th over a couple of visits, or whose weight suddenly stalls while their length keeps increasing, warrants a closer look. This kind of crossing is different from the gentle, gradual shifts that happen normally.
Thresholds That Flag a Problem
The WHO uses cutoff values at the 2nd and 98th percentiles (corresponding to 2 standard deviations below and above the median) to define potentially abnormal growth. In practical terms:
- Below the 2nd percentile for weight-for-length: considered low weight-for-length, which can indicate recent malnutrition, dehydration, or an underlying condition
- Below the 2nd percentile for length-for-age: classified as short stature, which may reflect chronic undernutrition or a genetic condition
- Below the 5th percentile for weight-for-length or BMI-for-age: considered underweight or wasting
On the more severe end, dropping below 3 standard deviations below the median indicates severe underweight, severe stunting, or severe wasting, depending on which measurement is affected. These thresholds aren’t diagnoses on their own. They’re flags that prompt further evaluation.
Head circumference has its own significance. A head size tracking below the 2nd percentile or above the 98th percentile can signal conditions affecting brain development, though some children simply have heads that are smaller or larger than average without any underlying issue. The trend over time, again, is more informative than a single reading.
Weight-for-Length vs. BMI-for-Age
For children under 2, the WHO charts use weight-for-length rather than BMI. This measurement compares your baby’s weight directly against their body length, which is more practical and accurate when a child is too young to stand for a reliable height measurement. After age 2, BMI-for-age takes over as the standard metric for assessing whether a child’s weight is proportional to their size. The WHO provides separate weight-for-length charts for boys and girls from birth to 2, then switches to weight-for-height charts from ages 2 to 5.
What a Single Measurement Tells You
A single plot on the growth chart is a starting point, not an answer. It tells you where your child stands at one moment. The real value of growth charts comes from plotting multiple measurements over months and seeing the trajectory. A baby at the 5th percentile who has always tracked there is in a very different situation from a baby at the 5th percentile who was at the 50th percentile three months ago. For reference, a 24-month-old boy weighing about 26¾ pounds sits right at the 50th percentile on the WHO weight-for-age chart.
Growth charts are one tool among many. They don’t account for your child’s genetics, birth weight, or individual development milestones. A pediatrician considers all of these factors together when evaluating whether a child’s growth pattern is healthy. The chart provides the data; the full picture requires context.