Measurement of growth in children

1 INTRODUCTIONThe goal of nutritional assessment in childhood is to determine if there are growth abnormalities that point to the presence of an underlying disease and also to prevent nutritional disorders and the increased morbidity and mortality that accompany them. To meet these goals, pediatric clinicians must know the risk factors for obesity and malnutrition and must understand the normal and abnormal patterns of growth and the changes in body composition during childhood and adolescence. In addition, they must be able to accurately perform and interpret the results of the nutritional evaluation.Nutritional assessment is the quantitative evaluation of nutritional status. A comprehensive nutritional assessment has four components:●Dietary, medical, and medication history●Physical examination●Growth, anthropometric, and body composition measurements●Laboratory testsThe measurements of growth are reviewed here. The measurement of body composition, the dietary history, and clinical and laboratory features of nutritional disorders are discussed separately. (See'Measurement of body composition in children' and'Dietary history and recommended dietary intake in children' and'Malnutrition in children in resource-limited countries: Clinical assessment' and'Clinical evaluation of the child or adolescent with obesity' and'Laboratory and radiologic evaluation of nutritional status in children'.)2 GROWTH STANDARDSGrowth measurements are the most important components of the nutritional assessment of children because normal growth patterns are the gold standard by which clinicians assess the health and well-being of children. A normal growth pattern does not guarantee overall health; however, children with abnormal growth patterns frequently have nutritional complications of specific clinical disorders (eg, cystic fibrosis, inflammatory bowel disease) or poor socioeconomic conditions. Altered growth patterns are a late consequence of nutritional insult, regardless of the cause of nutritional deprivation. Thus, careful surveillance for nutrition problems, particularly in children who are at risk, is necessary for the prevention of nutritional morbidity. (See'Indications for nutritional assessment in childhood' and'Malnutrition in children in resource-limited countries: Clinical assessment'.)Height, weight, body mass index (BMI), and head circumference measurements are the mainstays of the nutritional assessment of the child. These measurements are useful only if the clinician is able to correctly interpret them by converting absolute values to relative standards for the appropriate reference population [1].Growth measurements should be plotted on growth charts that provide a reference for the population being measured. Serial measurements must be obtained to determine if the growth pattern is truly abnormal or is a normal variant. Normal variants of growth include constitutional short stature and the gradual movement between growth curves that sometimes occurs in healthy infants and children during the first 24 months of life (sometimes called 'rechanneling') (see'Diagnostic approach to children and adolescents with short stature', section on 'Normal growth'). Children whose length, height, or weight measurements fall below the 5th percentile, above the 95th percentile, or cross two major centile curves are at nutritional risk and merit further consideration. As an example, if a child's weight falls from the 25th to the 10th percentile during one year, the clinician should investigate for an explanation, including signs and symptoms of underlying disease. Growth is most rapid in healthy children during early infancy and adolescence. (See'Normal puberty' and'Normal growth patterns in infants and prepubertal children', section on 'Normal patterns'.)2.1 Centers for Disease Control and Prevention growth reference — In the United States, the Centers for Disease Control and Prevention (CDC) and National Center for Health Statistics (NCHS) have preparedgrowth charts based upon data from five national health examination surveys and five supplementary data sources.On these charts, the normal range is generally defined as between the 5th and 95th percentiles, although additional categories are also used (eg, defining a category of 'Overweight' between the 85th and 95th percentile).2.2 World Health Organization growth standards — The World Health Organization (WHO) developedgrowth standards through the WHO Multicentre Growth Reference Study to describe normal child growth from birth to five years under optimal environmental conditions [2,3]. These standards can be applied to all children everywhere regardless of ethnicity, socioeconomic status, and type of feeding. A pooled sample from six participating countries was used for the development of an international standard of growth. In addition, standardized BMI charts for infants to five years of age were developed. The reference lines on the WHO growth charts are either percentile lines or Z-scores; Z-scores are units of standard deviation (SD) from the population mean. (See'Z-scores' below.)On these charts, the normal range is generally defined as between -2 SD and +2 SD (ie, Z-scores between -2.0 and +2.0), which corresponds to approximately the 2nd and 98th percentiles (figure 1).figure1 Interpretation of Z-scores for growth parameters

BMI: body mass index; IMCI: Integrated Management of Childhood Illness.* Length (recumbent) is generally measured for children younger than 2 years of age, and height (standing) is measured for those 2 years and older.¶ A child in this range is very tall. Tallness is rarely a problem, unless it is so excessive that it may indicate an endocrine disorder such as a growth hormone-producing tumor. Refer a child in this range for assessment if you suspect an endocrine disorder (eg, if parents of normal height have a child who is excessively tall for his or her age).Δ A child whose weight-for-age falls into this range may have a growth problem, but this is better assessed from a weight-for-length/height or BMI-for-age.◊ A plotted point above 1 shows possible risk. A trend towards the 2 Z-score line shows definite risk.§ It is possible for a stunted or severely stunted child to become overweight.¥ This is referred to as very low weight in IMCI training modules[1].Reference:Integrated Management of Childhood Illness, in-service training. WHO, Geneva, 1997.Reprinted with permission from: World Health Organization. Training course on child growth assessment. WHO, Geneva 2008. Copyright © 2008 World Health Organization. Full publication available at: http://www.who.int/childgrowth/training/module_c_interpreting_indicators.pdf.The WHO standards define a population that is somewhat longer and leaner than the CDC/NCHS references; this discrepancy is most dramatic during mid- and late infancy [4,5]. When using the appropriate cutoffs (ie, the 5th and 95th percentile for the CDC charts and the 2.3rd and 97.7th percentiles for the WHO charts), the prevalence of shortness and overweight are similar for both charts (table 1) [5]. However, the prevalence of underweight (low weight-for-age or low weight-for-height) was lower when using the WHO charts than the CDC/NCHS charts. Thus, the main difference is that the WHO standards are less likely to categorize a child as undernourished as compared with the CDC/NCHS growth references [4,5]. This probably is because the WHO standards were derived from multiple countries, including those that have a lower obesity rate than the United States, whereas the CDC growth references are derived from the United States' population.table1 Comparison of National Center for Health Statistics and World Health Organization growth charts for childrenYear publishedNCHS/CDCWHO20002006Population(s) from which curves were derivedGeneral United States population (data from the National Health and Nutrition Survey between the 1970s and 1990s); includes infants and children from a variety of socioeconomic and ethnic groupsMulticentre Growth Reference study (Brazil, Ghana, India, Norway, Oman, United States); population chosen to reflect growth under ideal conditionsAge groups0 to 36 months (cross-sectional data; includes both breastfed and formula-fed infants)2 to 20 years (cross-sectional data)0 to 2 years (longitudinal data); infants were exclusively/predominantly breastfed for 4 to 6 months and continued to breastfeed until at least 12 months2 to 5 years (cross-sectional data)Estimated prevalence of overweight in United States children*¶0 to 23 months9.6%7.5%24 to 59 months9.6%8.5%Estimated prevalence of underweight in United States children*ΔWeight-for-age0 to 23 months6.8%2%24 to 59 months3.8%0.8%Weight-for-height0 to 23 months4%0.8%24 to 59 months3%0.5%Estimated prevalence of shortness in United States children*◊0 to 23 months4.9%5.2%24 to 59 months2.9%3.1%NCHS: National Center for Health Statistics; CDC: Centers for Disease Control and Prevention; WHO: World Health Organization; BMI: body mass index.* Using data from the National Health and Nutrition Examination Survey (1999 to 2004).¶ On the NCHS curves, overweight is defined by weight-for-height >95th percentile for children 0 to 23 months and BMI >95th percentile for children 24 to 59 months. On the WHO curves, overweight is defined by weight-for-height >97.7th percentile for children 0 to 23 months and BMI >97.7th percentile for children 24 to 59 months.Δ On the NCHS curves, underweight is defined by weight-for-age or weight-for-height <5th percentile. On the WHO curves, underweight is defined by weight-for-age or weight-for-height <2.3rd percentile.◊ On the NCHS curve, shortness is defined by height-for-age <5th percentile. On the WHO curve, shortness is defined by height-for-age <2.3rd percentile.The WHO charts are considered a growth standard because they describe children raised under optimal nutritional conditions. By contrast, the CDC charts are considered a growth reference because they include children raised in a variety of nutritional conditions in the United States.2.3 Recommended growth charts — As of September 2010, theCDC recommends using curves based on the WHO child growth standards for infants and toddlers under two years of age and the CDC/NCHS growth references for children two years and older [1,6].This approach may cause some children to change categories when they reach 24 months of age (eg, a child may be classified as overweight on the WHO charts at 24 months but normal weight on the CDC charts). In addition, clinicians should transition from measuring recumbent length to standing height at 24 months of age to match the standard on which each chart is based because measurements of recumbent length are approximately 1 cm greater than measurements of stature [6]. (See'Length or height' below.)This recommendation reflects the opinion that the WHO charts represent a healthier standard for children younger than two years of age because they are based on longitudinal measurements in a breastfed population. Use of the WHO charts is less likely to lead to miscategorization of a breastfed baby as being underweight [6] (although that may not be the case for infants younger than six months of age [7]). The CDC and the American Academy of Pediatrics (AAP) are collaborating to develop additional guidance for appropriate use of these growth charts for monitoring growth within the United States' population.2.3.1 Infants 0 to 2 years — On these WHO charts, the normal range is generally defined as between -2 SD and +2 SD (ie, Z-scores between -2.0 and +2.0), which corresponds to approximately the 2nd and 98th percentiles.●Length (figure 2A-B)●Weight (figure 3A-B)●Weight-for-length (figure 4A-B)●Head circumference (figure 5A-B)Charts combining these curves are also available and may be most practical for clinical use:●Weight-for-age and length-for-age (males;females)●Weight-for-length and head circumference (males;females)2.3.2 Children and adolescents 2 to 20 years — On theseCDC/NCHS growth charts, the normal range is generally defined as between the 5th and 95th percentiles, although additional categories are also used (eg, defining a category of 'Overweight' between the 85th and 95th percentile).●Height (figure 6A-B)●Weight (figure 7A-B)●BMI (figure 8A-B)Charts combining these curves are also available and may be most practical for clinical use:●Weight-for-age and height-for-age (males;females)●BMI (males;females)The above height-for-age curves reflect children with average timing of pubertal development. For selected children with early or delayed puberty, the appropriateness of current height and the child's height potential may be more accurately assessed by using curves selected for the child's stage of pubertal development. (See'Tanner stage-adjusted height reference' below.)2.3.3 Preterm infants — For preterm infants up to approximately 10 weeks post-term, other growth references should be used, as discussed in a separate topic review. (See'Growth management in preterm infants', section on 'Growth chart'.)2.4 Z-scores — Height/length and weight measurements may be converted to Z-scores, which are values that represent the number of SDs from the mean height and weight values for age (figure 1). A child whose Z-score for height/length for age is <-2 (more than 2 SDs below the mean) has short stature. The evaluation and management of such a child differs with the clinical setting: If the child lives in a population where undernutrition is common (eg, in a resource-limited country), then the evaluation and management focuses on this issue (see'Malnutrition in children in resource-limited countries: Clinical assessment'). If the child lives in a population where undernutrition is not common, the evaluation for short stature includes considerations of a variety of causes. (See'Diagnostic approach to children and adolescents with short stature'.)A child whose Z-score for weight-for-height/length is <-2 is underweight. If the child lives in a population where malnutrition is common, then the management focuses on restoring nutrition and treating underlying infections. If the child lives in a population in which malnutrition is not common, the evaluation focuses on diagnosing and treating other conditions that might be responsible for the poor weight gain. (See'Malnutrition in children in resource-limited countries: Clinical assessment' and'Management of complicated severe acute malnutrition in children in resource-limited countries' and'Poor weight gain in children older than two years in resource-rich countries', section on 'Diagnostic approach' and'Poor weight gain in children younger than two years in resource-rich countries: Etiology and evaluation', section on 'Definitions'.)Most clinicians do not use Z-scores routinely, because growth abnormalities can be identified readily by plotting height and weight measurements on the standard growth charts. However, the use of Z-scores is particularly helpful when assessing the growth delays of the child whose height and weight measurements fall well below or above standard percentile values or when comparing populations that use different standards. Charts and calculators that facilitate the use of Z-scores are available in the linked topic review. (See'Malnutrition in children in resource-limited countries: Clinical assessment'.)2.5 Calculators — Z-scores and percentiles may be calculated using the following calculators. Similar to the growth curves above, these calculators are based on WHO reference data for infants and children younger than two years of age and on the CDC population standards for children and adolescents older than two years of age:●Infants 0 to 2 years:·Weight (calculator 1)·Recumbent length (calculator 2)·Weight-for-length (calculator 3)●Children and adolescents 2 to 20 years:·BMI for males (calculator 4)·BMI for females (calculator 5)·Weight for males (calculator 6)·Weight for females (calculator 7)·Standing height for males (calculator 8)·Standing height for females (calculator 9)2.6 Tanner stage-adjusted height reference — A series of Tanner stage-adjusted (TSA) height reference curves has been developed that reflect height-for-age at each stage of pubertal development, based upon data from the United States population [8]. The primary clinical utility of these curves is for:●Children with short stature with late puberty for their age – This includes children whose puberty is delayed because of medical illness or puberty-suppressing therapy. For these children, use of standard CDC height-for-age growth curves may exaggerate their degree of short stature. (See'Diagnostic approach to children and adolescents with short stature' and'Approach to the patient with delayed puberty'.)●Children with tall stature with early puberty for their age – For these children, use of standard CDC height-for-age growth curves may exaggerate their degree of tall stature. (See'The child with tall stature and/or abnormally rapid growth' and'Definition, etiology, and evaluation of precocious puberty'.)For these children, current growth status and growth potential may be more accurately assessed by using a TSA height reference, which is captured in thisonline calculator or by plotting the child's growth on aTSA-adjusted height-for-age growth curve, selected for their stage of pubertal development (sexual maturity rating) [8].3 LENGTH OR HEIGHTLength or height measurements require a firm, flat, horizontal, or vertical surface with perpendicular surfaces at each end [9]. Length is measured in children younger than two years who are measured in the recumbent position (figure 2A-B). Height or stature is measured in children older than two years who are measured while standing (figure 6A-B). Length and stature should be measured to the nearest 0.1 cm [10]. Ideally, the measurement should be performed three times to improve accuracy, and the mean should be plotted on a standardized growth chart. Length and height measurements are susceptible to variability due to operator error. Measurements that are not clinically plausible (eg, decreases in a child's height) should be repeated and corrected as necessary. These growth charts presume a transition from measuring recumbent length to standing height at two years of age. For a given individual, measured length is approximately 1 cm greater than standing height.Estimates from knee height — Alternative measurements to monitor linear growth for children with spinal deformities or extremity contractures include upper arm length and knee height [10-13]. Standard curves exist for these measurements [12,13]. Knee height is the distance from the surface of the thigh, just proximal to the patella, to the sole of the foot when the knee and the foot are bent at a 90º angle. Knee height is measured with a caliper designed for this purpose. Equations to estimate the height in cm from the knee-height measurement for children 6 to 18 years include the following [12]:●White children:Males: height = 40.54 + (2.22 × knee height)Females: height = 43.21 + (2.15 × knee height)●Black children:Males: height = 39.60 + (2.18 × knee height)Females: height = 46.59 + (2.02 × knee height)A second alternative is to use the following equation (based on data from children with cerebral palsy and younger than 12 years of age) [14]:Height = 24.2 + (2.69 × knee height)Children with severe cerebral palsy may have significant deviation from true length/height due to contractures or spinal deformities. Direct measurement of length in the supine position is the best way to accurately monitor growth in the clinical setting for some of these patients [15].4 WEIGHTWeight measurements should be obtained on a scale that has been calibrated properly. The infant should be weighed without diapers and to the nearest 0.01 kg [10]. The older child should be measured without shoes, in little or no outer clothing, and to the nearest 0.1 kg. The measurement should be plotted on a standardized growth chart (figure 3A-B andfigure 7A-B).The World Health Organization (WHO) curves are more appropriate than the Centers for Disease Control and Prevention (CDC) and National Center for Health Statistics (NCHS) curves for plotting the growth of exclusively breastfed infants during the first year of life since the WHO curves were derived from a breastfed population. As compared with formula-fed infants, infants who are exclusively breastfed tend to have more rapid weight gain during the first three months of life, then slower weight gain thereafter. (See'World Health Organization growth standards' above and'Normal growth patterns in infants and prepubertal children', section on 'WHO growth charts'.)5 BODY MASS INDEXThe body mass index (BMI) characterizes the relative proportion between the child's weight and height. It is a valid predictor of adiposity and is therefore the best clinical standard for defining obesity in adults and in children older than two years of age.The BMI is calculated from the weight and square of the height as follows:BMI = body weight (kg) ÷ height (meters) squaredBMI varies with age, gender, and pubertal stage, so growth standards are based on BMI percentiles. The calculated BMI is plotted on a BMI reference chart to determine the BMI percentile (figure 8A-B). The BMI and percentiles can be determined using a calculator for males (calculator 4) and for females (calculator 5).A child with a BMI greater than the 85th percentile is overweight, and a child whose BMI is greater than the 95th percentile is obese. The evaluation of a child with high BMI percentiles is discussed in detail separately. (See'Clinical evaluation of the child or adolescent with obesity'.)BMI standards for underweight are less well defined, but children with a BMI less than the 5th percentile are underweight and should be evaluated and monitored for nutritional abnormalities. In undernourished adolescents, such as those with anorexia nervosa, BMI tends to underestimate the degree of malnutrition as compared with weight-for-height measurements [16]. However, no studies have examined whether one of these two methods better predicts clinical outcomes. Other methods can measure adiposity directly but have limited utility in the clinical setting. (See'Measurement of body composition in children'.)6 WEIGHT-FOR-HEIGHTLike body mass index (BMI), the ratio of weight to height can be used to predict adiposity.For children aged 0 to 2 years, the ratio of weight to length generally has been used instead of BMI (figure 4A-B) (calculator 3). However, there is increasing evidence that BMI may be more reliable than the ratio of weight to length in children 0 to 2 years of age. This is in part because BMI charts take age into account, whereas the weight-to-length charts do not. As an example, one study found that BMI Z-scores are more closely associated with adiposity than weight-for-length Z-scores in healthy one-month-old infants. Whether BMI during infancy is a better predictor of childhood obesity than weight-for-length remains unclear [17-19]. (See'Poor weight gain in children younger than two years in resource-rich countries: Etiology and evaluation', section on 'Measurement of growth'.)For children aged three to five years, BMI for age and weight-for-height measures predict adiposity equally well. Nonetheless, BMI is generally used for assessing an overweight child because most risk thresholds and clinical recommendations have been based on the BMI percentiles (using the Centers for Disease Control and Prevention [CDC] reference charts). A child's weight-for-height can be compared with normal standards using a chart with CDC reference (weight-for-stature for boys orweight-for stature for girls) or World Health Organization (WHO) standards (figure 9A-B).For children aged 6 to 19 years, BMI for age is slightly better than weight-for-height in predicting adiposity [20]. (See'Body mass index' above.)7 HEAD CIRCUMFERENCEThe head circumference is measured at the maximum diameter through the glabella and occiput to the nearest 0.1 cm. The recorded value should be the mean of three measurements [10]. Head circumference is measured in children from birth to three years of age because this is the period of rapid brain growth. Head circumference also should be measured in older children with abnormal growth because it may be helpful in determining the etiology. A child with fetal alcohol syndrome, as an example, may have growth deficiency and microcephaly. The measurement should be plotted on a standardized growth chart.Abnormal head growth is defined as a head circumference (also called fronto-occipital circumference) >2 standard deviations (SD) above or below the mean for a given age, gender, and gestation.●Microcephaly is a head circumference >2 SD below the mean (figure 5A-B) (calculator 10)●Macrocephaly is a head circumference >2 SD above the meanThe evaluation and interpretation of abnormal head growth is discussed in detail separately. (See'Microcephaly in infants and children: Etiology and evaluation', section on 'Postnatal evaluation' and'Macrocephaly in infants and children: Etiology and evaluation', section on 'Evaluation of postnatal macrocephaly'.)8 GROWTH VELOCITYIncremental growth charts that characterize height and weight velocities over time are valuable in assessing the growth of children, particularly those with specific clinical disorders [21-24].●Height velocity measurements are the most sensitive in detecting growth abnormalities early in the course of all types of chronic illness [25]. Any child older than two years whose height velocity is less than 4 cm/year should be monitored carefully for progressive nutritional deficits or causes of short stature because at least 95 percent of children grow faster than 4 cm/year [26]. During puberty, peak height velocity is 6 to 12 cm/year in males and 5 to 10 cm/year in females; the age of peak height velocity varies substantially (figure 10A-B). (See'Diagnostic approach to children and adolescents with short stature'.)●Any prepubertal child whose weight velocity is less than 1 kg per year should be monitored carefully for progressive nutritional deficits because approximately 95 percent of children gain weight faster than this rate in a well-nourished population [27]. During puberty, weight gain is more rapid; peak weight velocity is generally between 1 and 4 kg per six months in a healthy population.9 FURTHER ASSESSMENT9.1 Malnutrition — The degree of acute and chronic malnutrition, characterized as ponderal wasting and linear stunting, respectively, can be assessed clinically using various anthropometric measurements (table 2). The assessment methods are based upon the assumption that during periods of nutritional deprivation, weight deficits occur initially, followed by length or height deficits and finally by head circumference deficits. Estimates of the severity and duration of nutritional deprivation provide guidelines for the nutritional rehabilitation of the malnourished child [28]. Definitions of malnutrition based on growth measurements are discussed in detail separately. (See'Malnutrition in children in resource-limited countries: Clinical assessment'.)table2 Methods for classification of the severity of malnutritionMethod0Normal1Mild2Moderate3SevereNutritional implicationsWeight-for-height, percent expected*[1,2]≥90<90<80<70WastingHeight-for-age, percent expected*[1,2]≥95<95<90<85StuntingMUAC/FOC¶[3]≥0.31<0.31<0.28<0.25WastingThese methods are presented here for completeness, but they are no longer recommended for the assessment of the severity of malnutrition. Instead, the WHO recommends use of Z-scores for length/height, weight, and clinical assessment of edema (refer to topic text for details).MUAC: mid-upper arm circumference; FOC: fronto-occipital circumference.* The percent of median method is also known as a modified Waterlow method.¶ This is also known as the McLaren method; it is used to assess acute malnutrition in children younger than 3 years of age when accurate measures of height and weight cannot be obtained.Adapted from: 1. Waterlow JC. Classification and definition of protein-calorie malnutrition. Br Med J 1972; 3:566. 2. Waterlow JC. Note on the assessment and classification of protein-energy malnutrition in children. Lancet 1973; 2:87. 3.Kanawati AA, McLaren DS. Assessment of marginal malnutrition. Nature 1970; 228:573.The treatment of malnutrition in children is discussed separately. (See'Management of uncomplicated severe acute malnutrition in children in resource-limited countries' and'Management of complicated severe acute malnutrition in children in resource-limited countries' and'Poor weight gain in children younger than two years in resource-rich countries: Management', section on 'Initial management'.)9.2 Obesity — The clinical evaluation of a child with obesity includes assessment of the body mass index (BMI) or weight-to-height ratio percentile and trend, potential weight-related comorbidities, and potential environmental and endocrine contributors to the obesity. Precise measurement of the body fat content is not generally necessary or helpful for clinical decision-making. (See'Clinical evaluation of the child or adolescent with obesity' and'Measurement of body composition in children'.)9.3 Short or tall stature — Radiographic studies of bone age can help to clarify the presence of abnormal growth patterns. Chronic undernutrition, for example, is one of the causes of delayed bone maturation and delayed linear growth [29]. However, bone age assessments may be less helpful in the young child because of the variability of normal bone development in this age group. (See'Diagnostic approach to children and adolescents with short stature' and'Poor weight gain in children younger than two years in resource-rich countries: Etiology and evaluation', section on 'Growth trajectory and proportionality'.)INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, 'The Basics' and 'Beyond the Basics.' The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on 'patient info' and the keyword(s) of interest.)●Basics topic (see'Patient education: My child is short (The Basics)')SUMMARY AND RECOMMENDATIONS●The growth charts developed by the Centers for Disease Control and prevention (CDC) were developed from large surveys of multiethnic populations and are appropriate references for individuals living in the United States. (See'Centers for Disease Control and Prevention growth reference' above.)●The standards developed by the World Health Organization (WHO) describe normal growth from birth to five years under optimal environmental conditions, including breastfeeding. These standards can be applied to all children everywhere regardless of ethnicity, socioeconomic status, and type of feeding. As compared with the reference prepared by the CDC, the WHO standards result in lower estimates of undernutrition, except during the first six months of life, and higher rates of obesity. (See'World Health Organization growth standards' above.)●For children in the United States, recommended growth charts are based upon WHO data for children younger than two years of age and on CDC data for those older than two years. (See'Recommended growth charts' above.)·Infants 0 to 2 years:-Length (figure 2A-B)-Weight (figure 3A-B)-Weight-for-length (figure 4A-B)-Head circumference (figure 5A-B)·Children and adolescents 2 to 20 years:-Height (figure 6A-B)-Weight (figure 7A-B)-Body mass index (BMI) (figure 8A-B)●Z-scores describe the degree to which a measurement deviates from the mean of a population standard (figure 1). Z-scores are particularly useful for measurements at the extremes of a distribution (<3rd or >97th percentile). The WHO classification of malnutrition is based on Z-scores. On the WHO charts, the normal range is defined as Z-scores between -2.0 and +2.0 (ie, between -2 standard deviations [SD] and +2 SD). Thus, underweight is defined as a weight-for-height/length Z-score <-2. (See'Z-scores' above.)●Linear growth is determined by length in children younger than two years and is measured in the recumbent position. Linear growth is determined by height (stature) in children older than two years and is measured while standing. These measures are plotted on a standard growth chart. (See'Length or height' above.)●Weight is typically plotted against standards prepared by the CDC. The WHO curves are more appropriate than the CDC/National Center for Health Statistics (NCHS) curves for plotting the growth of exclusively breastfed infants during the first year of life since the WHO curves were derived from a breastfed population. (See'Weight' above.)●BMI characterizes the relative proportion between the child's weight and height. Because it is correlated with adiposity, it is used as the clinical standard for determining obesity (figure 8A-B). The BMI also can be determined using a calculator for males (calculator 4) and for females (calculator 5). (See'Body mass index' above and'Obesity' above.)REFERENCESKuczmarski RJ, Ogden CL, Grummer-Strawn LM, et al. CDC growth charts: United States. Advance data from vital and health statistics. Number 314. National Center for Health Statistics; Centers for Disease Control and Prevention, Hyattsville, MD 2000.World Health Organization. The WHO Child Growth Standards. Available at: www.who.int/childgrowth/standards/en/ (Accessed on February 27, 2008).WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards based on length/height, weight and age. Acta Paediatr Suppl 2006; 450:76.de Onis M, Garza C, Onyango AW, Borghi E. Comparison of the WHO child growth standards and the CDC 2000 growth charts. J Nutr 2007; 137:144.Mei Z, Ogden CL, Flegal KM, Grummer-Strawn LM. Comparison of the prevalence of shortness, underweight, and overweight among US children aged 0 to 59 months by using the CDC 2000 and the WHO 2006 growth charts. J Pediatr 2008; 153:622.Grummer-Strawn LM, Reinold C, Krebs NF, Centers for Disease Control and Prevention (CDC). 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