For many years, the growth reference data of Chinese children and adolescents was obtained from the two series of national surveys, the NSPGDC for preschool children aged 0–7 years and the CNSSCH for school children aged 7–18. These data was routinely updated every 10 years under the secular trends. However, the practical application of those raw reference data in growth monitoring and nutrition assessment was limited, due to the lack of convenient age intervals, the shortage of smoothed percentiles and SD curves, the absence of continuity at the entire age range (separate at age 6–7 years) and the incompleteness of indicators. Therefore, it was necessary to construct a standardized growth curves for Chinese children and adolescents in new century, based on up-to-date national data using the international smoothing method.
The rapid positive secular growth trends will continue in China as the rapid socio-economic development going on 
. The growth level of urban children was successively taller than suburban ones 
. The urban data has been widely used as the most representative reference values in many fields since 1975. So, we merged the data from the 4th
NSPGDC (0–7 years) with the 5th
CNSSCH (6–20 years) into a complete age group to generate the growth curves from birth to 18 years. The reference sample was urban children and adolescents which were representative of healthy, relatively well-nourished population who were born and raised under good conditions with the high living standards and education level in China. In the sample population, the proportion of receiving high school education and above was 84.4% for their fathers and 80.6% for mothers 
and the overall breast-feeding rate was 85.1% for infants below 4 months and exclusive breast-feeding 47.7% 
The two comments of the advisory panels benefited the construction of the China references. The first was that data from the corresponding 9 provinces/cities of the 5th CNSSCH was naturally selected for merging with data from the 4th NSPGDC because those regions were nearly the same geographical positions and relative high socioeconomic background as the 9 cities of the latter. The second was that urban children were selected as the reference sample to develop the curves due to the differences of growth among urban, suburban and rural areas and the growth potential of Chinese children under the rapid secular trends.
Human growth differs throughout history. Data from the Chinese surveys showed the rapid secular growth trends during the past decades 
. The positive trends reflected the great socioeconomic development after the economic reform and opening up. It had effected greatly the construction and application of the China references. The previous reference data, national or local, had obvious historical limitations in evaluating current performance of growth and nutrition of children and adolescents. The China references provided by this study were the updated standardized national reference values under the positive secular trends and could truly estimate the level of growth and nutrition in current stage.
Human growth differs among the various ethnic groups. The differences of the standards/references among regions or countries were largely caused by the respective reference populations. They might partly be attributed to the study designs (e.g. exclusion criteria, measurement tools and age group intervals) and the smoothing methods. Growth pattern was similar in different ethnic populations, but the differences of the standards/references could not be neglected in practical application, especially for the assessment of individual child. Followings are the main differences and interpretations between China and WHO founded in this study.
The gender difference was very obvious. Chinese boys were appreciably heavier than girls at counterpart age, which was also funded in other studies 
. For weight and weight related indicators, the nutrition level of Chinese girls was generally lower than that of Western countries, but usually not for boys. For example, boys’ BMI at age 6–16 years in China was higher than their counterparts in the WHO, but girls’ BMI 3–18 years was lower, especially on the +2 SD curve. The reversal performance was also observed in overweight and obesity studies among Chinese children, i.e. the prevalence rates for boys significantly higher than girls’ 
. Another study, data not from the two series of surveys, also showed the same gender performance 
. Compared with the Western, the gender-specific performance was an interesting fact, which may be associated with a bigger percentage of the “fat” population in boys and the traditional Chinese cultural and social values. The trend analysis of overweight and obesity in Chinese students during 1985–2010 showed the prevalence rates in boys were higher than those in girls in urban and rural areas 
. In other words, the “fat” population has a bigger percentage in boys than in girls. In the traditional Chinese culture, boys were expected to be tall and strong so that they can be the major labor force of a family when they grow up. On the opposite, girls were expected to be slim and elegant. If they were too fatty and strong, it may have negative effect of their marriage in the future. So girls and their family may choose to select and limit their daily diet.
Final heights of Chinese populations are significantly shorter than that of the WHO (i.e. U.S. samples) in males and females. The Chinese are taller until adolescence, but then being shorter as adults. This cross-over performance reflects another obvious ethnic characteristic. The taller performance before puberty may be related to the rapid increasing growth trends in the past decades and also the earlier and earlier onset age of puberty, such as earlier 0.2 year per decade between 1985 and 2005 
. After 15-year-old for boys and 13-year for girls, the growth sharply slowed down and the average residual growth potential was about 3–4 cm. Their height was close to adult height in boys after 16-year and in girls after 15-year. The varying performance over age among different regions or countries strongly supports the necessity of establishing population-specific references.
The differences in boundary curves (e.g. −2 and +2 SD) are also interesting for each indicator. The Chinese boys are fatter than the WHO for BMI at nearly all ages (with the exception of ages 4–6 where the curves cross over) and later adolescence. The +2 SD curves for the Chinese and WHO cross at age 17, showing that they reach the same BMI but following quite different routes to get there. The Chinese girls are heavier than the WHO’s in early life, particularly on the lower centiles, but the age at adiposity rebound is appreciably later and the later curves are much lower. Cole & Lobstein 
described the cross-over pattern of WHO that was relatively low in early life and relatively high later as a feature of the WHO standard/reference. De Onis et al 
suggested the performance of BMI partly reflected the nutrition status of sample and probably there were also some edge effects by comparison of the WHO standards and the CDC 2000 charts. The differences of BMI reflected data sources used by the Chinese and the WHO. Thus, estimates of overweight/obesity might be somewhat different for genders and age groups using the empirical “cut-off points” of the different standards/references.
The disparity of estimated prevalence rates in shortness, underweight, and overweight/obesity might be the differences of boundary centiles between China and WHO. A study written by Mei et al 
showed estimates of prevalence of key descriptors of growth varied by the chart used and the cutoff values applied which suggested the charts and cutoff values would be a change for office practice. Therefore, for practitioners, the WHO standards might be a better tool for the purpose of comparisons among countries/regions. More attention should be given to further explore the variation of growth among race/ethnicity groups and the practical applications in clinic and public health.
China is a big country, stretching from north latitude 4° to 53° and east longitude 73° to 135° with the disparity of the regional socioeconomics in current stage. The genetic growth potential may vary among different geographical regions and socioeconomic classes. The series of the NSPGDC shows that no sufficient evidence supported the regional growth difference in inter-province/city was reducing 
. Urban-suburban-rural difference had a narrowing trend but the gap did not disappear according to the systematic analysis of the NSPGDC and another national survey undertaken in rural areas 
. The series of the CNSSCH displays the height growth rate of Chinese students is influenced by the geography and natural environment. The growth level in eastern China is higher than central-western, successively higher than southern 
. And the growth level in northern is higher than that in southern 
. So, from the perspective of socioeconomic classes, this new China references are a “current” reference for urban children and may be an “ideal” standard for suburban and rural children. From the geographic location, the China references are “current” for northern and eastern and may be an “ideal” for central-western and southern.The new China references are the first, multi-indicators, complete age range, smoothed growth reference values which will benefit more than 300 million Chinese children and millions of children of Chinese origins. The present study strongly suggests the China references are obviously advantageous in monitoring and assessing current performance of growth and nutrition of Chinese children and adolescents when compared with other standards or references, especially for individual growth monitoring in clinical practice. The set of references should help to promote the standardization assessment of growth and nutrition throughout the entire childhood in China.