There are two different sources of data available for normal child development: American data from the CDC, and international data from the WHO. For many reasons (detailed below), the WHO data is now the standard in most countries.
WHO (World Health Association)
The World Health Association recognized the need for a global standard of growth, based on global data of healthy children. The children were all full-term (born between 37 and 42 weeks), single pregnancies (not twins or other multiples), apparently healthy, predominantly breastfed (until at least 4 months, then at least partially breastfed until 12 months), immunized with all routine immunizations, and had introduction of complementary foods between 4 and 6 months of age. Essentially, these were (and largely still are) considered optimal conditions for growth. The data was released in 2006 and 2007, and has quickly become the standard for growth tracking in most countries. Their charts may be used for any aged child from any ethnic background. Because they demonstrate optimal, rather than simply describe typical growth, they are considered a growth standard.
For the WHO charts and data, please see the Resources page.
For more information, from a Canadian context, on why the WHO charts are used instead of the CDC chart, please see the following collaborative statement from the Canadian Pediatric Society, the Dietitians of Canada, the College of Family Physicians of Canada, and the Community Health Nurses of Canada: PROMOTING OPTIMAL MONITORING OF CHILD GROWTH IN CANADA: USING THE NEW WHO GROWTH CHARTS
CDC (Centers for Disease Control and Prevention)
These charts are an updated version of data initially collected in surveys on American children (aged 2-18) between the years of 1963-1974 by the American National Center for Health Statistics (NCHS). This data was descriptive, meaning it simply reflected the growth trends of the children surveyed during those years. Other than simply describing typical growth of the time, rather than optimal growth, this data set has often been criticized for the high rates of formula feeding (rather than breast feeding) in infants.
Within the US, this is the normal data set for children over the age of 2 years. Under the age of 2, the CDC and the American Pediatric Association recommend using the WHO data, as the CDC's data is not felt to reflect ideal growth for children under the age of 2.
For the CDC charts and data, please see the Resources page.
Special growth considerations
Children who do not meet the same criteria as the WHO surveys (ie, those not healthy, born prematurely or late, are multiples, or those with genetic abnormalities) may not tend to follow the same growth patterns as is reflected in the WHO charts. As such, some adjustments may be necessary.
Children born prematurely (before 37 weeks gestation) should have their growth adjusted for their predicted due date. Prior to this due date, a premature growth chart may be used, should one be available. After this, their age should be adjusted for how early they were born (40 weeks - age in weeks of their birth). [In this application, simply enter their due date as their birth date once the due date has past] The age adjustment should be continued for one year if the child was born between 32 and 36 weeks, or two years if born prior to 32 weeks of development.
Children with certain genetic syndromes (such as Down's Syndrome) do not follow the same growth patterns as the general population, and pose a challenge in interpreting growth if plotted against the general population curves. As such, there are modified growth charts available for this population that will eventually be accessible from this website.