From babyhood through toddlerhood and beyond, height, weight, head circumference, and body mass index (BMI) often take center stage during well-child visits. But what are those “growth charts” that pediatricians rely on, and how did they come to be the standard on which your child’s statistics are plotted? How children should grow has been the subject of a great deal of study over the years, with recent groundbreaking research being published on normal growth, from fetal development during pregnancy through 5 years of age.
A team of researchers led by experts from England’s Oxford University focused on babies’ growth in utero and at birth. Using a multi-site approach that was developed by the World Health Organization (WHO) for its work on growth standards for children 0–59 months of age, the INTERGROWTH-21st Project team focused on understanding babies’ first 100 days of development. Funded by the Bill and Melinda Gates Foundation, the study was undertaken in urban areas in eight diverse countries: Brazil, Italy, Oman, U.K., U.S., China, India, and Kenya. From May 2009 to August 2013, more than 20,000 women with low-risk, singleton (one baby) pregnancies and a reliable ultrasound estimate of gestational age early in pregnancy were recruited for the study. Based on their assessment of length, birth weight, and head circumference of babies born between 33 and 42 weeks’ gestation, the researchers developed a measure of infant health, malnutrition, or over-nutrition. The tool is intended, study researcher Professor Stephen Kennedy explains in an Oxford University press release, to “describe how babies in the womb should grow when they are provided with good health care and nutrition and are living in a healthy environment.”
The INTERGROWTH-21st Project figures have yet to be endorsed by U.S. officials, but experts believe that the data published in the team’s “Basic Neonatal Care Manual,” will be merged into current infant growth standards.
A history of growth charts
The framework for the INTERGROWTH-21st Project was based on work by the World Health Organization (WHO) to develop growth charts based on how children should grow, under healthy conditions.
Growth charts have long been a tool used by pediatricians and parents as a measure of health and wellbeing of children, but for many years the charts that were used were based on a small population of predominantly formula-fed children. Because infants grow differently on formula than they do on human milk, decisions made based on “appropriate” growth were often skewed. Breastfed infants tend to gain weight faster in the first 3–4 months, but are generally leaner than their formula-fed counterparts by 12 months. This caused concern for many breastfeeding parents throughout the first year, as their baby’s charted growth seemed to dive from growing “too fast” to “too slow.”
In 2006, WHO released a new set of growth charts for children 0–59 months, based not on how children do grow, but instead on how they ought to grow. The WHO standards were based on prospective data from a diverse population of babies who were given optimal, physiologically normal nutrition (i.e. infants were exclusively breastfed for six months), after which age- and culturally-appropriate complementary foods in addition to human milk were provided. Although it took a few years for researchers to accept the new standards, in 2010, the U.S. Centers for Disease Control and Prevention (CDC) issued a statement recommending that health care providers use the charts for all infants, acknowledging that the growth of breastfed babies is the standard against which all infant growth should be compared.
The CDC recommends that health care providers use WHO growth standards (which are also available on the CDC website) for children in the U.S. from ages 0–2 years, and the long-standing CDC growth charts for children 2 years and older. Although the WHO charts can be used for children up to age 5, the CDC recommends switching to the CDC charts when a child is 2 years old. The CDC charts can be used continuously for children ages 2–19 years, and for children 2–5 years, the methods used to create the CDC charts are similar to those used for the WHO charts.
Using the WHO Growth Standards
The CDC cites three reasons for using the WHO Growth Standards with U.S. children under 2 years of age:
- The WHO standards assume that breastfeeding is the norm. Their charts are based on the growth of children who were predominantly breastfed for at least 4 months, and who were still breastfeeding at 12 months.
- The WHO standards reflect a more accurate description of physiological growth during infancy. Earlier U.S. charts were based on how typical U.S. children grew during a time when most were formula-fed. These “typical” patterns were not necessarily “ideal” growth patterns.
- The WHO standards are based on a “high-quality study designed explicitly for creating growth charts.” Older charts were based on a small number of children for the first 6 months of age, and had no weight data for the first 3 months. In contrast, the WHO standards used nearly 8,500 children from six countries (Brazil, Ghana, India, Norway, Oman, and the U.S.), and measured longitudinal length and weight data frequently.
Growth charts are tools—one that should be used as part of a complete set of diagnostics to determine adequate and appropriate growth in children. A growth chart alone is not enough—family growth patterns and other indicators of good health and wellbeing are equally important. Also, charts are based on averages across a population. Unlike achieving a high score on a college entrance exam, being in the 95th percentile on a growth chart is not inherently better than being in the 10th percentile. Each child’s growth should be measured on his own chart over time, with attention paid to changes in the growth rate—as long as growth is steady and upward, a child who measures along the 14th percentile may be as healthy as a child who grows along the 74th percentile—as well as overall development physically, mentally, and behaviorally.
The growth charts
- Birth to 24 months: Boys Weight-for-length percentiles and Head circumference-for-age percentiles
- Birth to 24 months: Boys Length-for-age percentiles and Weight-for-age percentiles
- Birth to 24 months: Girls Weight-for-length percentiles and Head circumference-for-age percentiles
- Birth to 24 months: Girls Length-for-age percentiles and Weight-for-age percentiles
Additional charts for beyond 2 years of age are also available on the CDC website.