The World Health Organization (WHO) Child Growth Standards are comprehensive tools used globally to assess the physical growth and nutritional status of children from birth to age five. These standards provide a uniform, international reference for healthy development. Their primary goal is to establish a benchmark that helps health professionals and parents determine if a child is growing as expected under optimal environmental conditions. They are foundational for early detection of undernutrition, overweight, and other growth-related health problems across diverse populations.
Why the WHO Charts Are the Standard for Breastfed Babies
The WHO Child Growth Standards represent a significant shift from previous descriptive growth references. Older charts, such as historical references used in the United States, illustrated how a mixed population of children, often formula-fed, grew in a specific place and time. This data did not necessarily reflect ideal or optimal development. The new WHO charts are prescriptive, showing how children should grow when raised under conditions that favor good health.
This fundamental difference is rooted in the design of the WHO Multicentre Growth Reference Study (MGRS). Researchers followed thousands of healthy infants from six countries: Brazil, Ghana, India, Norway, Oman, and the United States. Strict inclusion criteria ensured these children were raised in environments without known growth constraints, such as maternal smoking or poor sanitation. The resulting charts reflect biological norms rather than the effects of suboptimal conditions.
Crucially, the study established breastfeeding as the biological norm for infant feeding and growth. All infants in the reference sample were breastfed for at least 12 months and predominantly breastfed for a minimum of four months. This focus acknowledges that the growth pattern of a breastfed infant naturally differs from that of a formula-fed infant.
Healthy breastfed babies typically gain weight more quickly in the first three to six months, but their weight gain tapers off in the second half of the first year. When plotted on older, formula-fed charts, this pattern often made breastfed infants appear to grow too fast initially and then “fail to thrive” later. By using the breastfed infant as the model, the WHO charts accurately reflect this physiological trajectory, providing a reliable assessment for all infants, regardless of feeding method.
Understanding the Key Metrics Tracked
The WHO charts measure several different anthropometric indicators, including weight-for-age, length-for-age, and head circumference-for-age. Length is measured while the child is lying down (recumbent length) up to age two, after which height is measured standing. These measurements are plotted on separate charts for boys and girls, as growth rates differ between sexes.
When a measurement is plotted on a chart, it falls on or between curved lines called percentiles. A percentile indicates where a child’s measurement ranks compared to the healthy reference population of the same age and sex. For example, if a child’s weight is on the 50th percentile, it means that half of the healthy infants in the reference group weigh less, and half weigh more. If a child is on the 15th percentile for length, it indicates that 15 percent of children are shorter, and 85 percent are longer.
The charts also provide indicators like weight-for-length and Body Mass Index (BMI)-for-age, which help assess proportionality and screen for possible overweight or wasting. Weight-for-length is useful in infancy for identifying disproportionate growth before age two. While BMI-for-age starts at birth, its use for screening for overweight is recommended for children two years and older.
For health professionals, the percentile lines themselves are less important than the overall direction of the plotted points, known as the growth trajectory or curve. A single measurement only shows a child’s size at one moment in time. Plotting a series of measurements over several months reveals the pattern of growth, which is a much stronger indicator of a child’s health status. A healthy growth pattern typically follows consistently along a single percentile curve or stays within a narrow band between two curves.
Interpreting Growth Patterns and Addressing Concerns
Parents often feel concern if their child is not near the 50th percentile, but this is a common misunderstanding of the charts. A child consistently tracking along the 10th percentile, for instance, is growing just as healthily as a child on the 90th percentile. The key factor is the consistency of the curve, which shows the child is growing at their own steady, predictable rate. Genetics, including the height and build of the parents, naturally influence a child’s growth trajectory.
Growth spurts and temporary plateaus are normal, particularly during times of illness or developmental milestones. A brief dip in weight gain, followed by a return to the child’s usual curve, is usually not a cause for concern. Health care providers look for a significant and sustained deviation from the established pattern.
Actionable signs that warrant a medical review include a rapid and sustained drop or climb across two major percentile lines. The WHO charts use the 2nd and 98th percentiles as the outermost cutoff points for defining abnormal growth. Falling below the 2nd percentile for weight-for-age or length-for-age may signal potential undernutrition or a chronic health problem.
Similarly, consistently tracking above the 98th percentile for weight-for-length or BMI-for-age may indicate a risk for overweight. These extreme percentiles signal that the child’s growth pattern is significantly different from the normative standard and requires further assessment. Consulting a health professional allows for a thorough evaluation that considers the child’s feeding history, parental stature, and overall well-being alongside the growth data.