Growth is influenced by a number of factors

Nutrition Behavior and Performance How Is Baby Doing? Growth of US and Canadian Infants Using the Centers for Disease Control and Prevention and Worl...
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Nutrition Behavior and Performance

How Is Baby Doing? Growth of US and Canadian Infants Using the Centers for Disease Control and Prevention and World Health Organization Charts Paul W. Ferguson, PhD Susan Hazels Mitmesser, PhD

P ediatricians typically use Centers for Disease Control and Prevention 2000 growth charts as reference tools to monitor and assess infant health and nutritional status. The World Health Organization 2006 growth charts, defined as a global growth standard, have been proposed for this use. To date, there are no longitudinal, prospective published data analyses for US and Canadian infants to evaluate the impact of adopting the World Health Organization charts. Because interventions are often driven by interpretation of weight percentiles, healthcare professionals need to be aware that the adoption of the World Health Organization 2006 growth charts may result in differences in infant weight categorization. The World Health Organization 2006 growth charts also include a body mass index chart for infants. Body mass index provides a reference used worldwide for classifying weight status in the older child and adult. However, it is not clear whether the body mass index chart is an appropriate screening tool to define infants younger than 2 years at risk for overweight and/or obesity. Nutr Today. 2007;42(4):151–159

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rowth is influenced by a number of factors including the intrauterine environment, genetic factors, and postnatal nutrition. A critical period for growth and development is from birth to 2 years.1,2 The consequences of poor nutrition during these years include compromised immunity, delayed motor and mental development, and stunted growth. Overnutrition may predispose infants to the risk for obesity, diabetes, and/or metabolic syndrome later in life. Therefore, appropriate assessment of optimal growth and nutrition during infancy and early childhood is vital. Growth charts are typically used to monitor growth and overall Nutrition Today, Volume 42



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Nirvarthi Maharaj, MD Carol Lynn Berseth, MD

infant health and nutritional status. Presently, the situation is confusing because 2 sets of growth reference charts are currently available: those published by the Centers for Disease Control and Prevention (CDC) in 20003 and those published by World Health Organization (WHO) in 2006.4 The CDC 2000 growth charts (birth to 36 months) are based on a compilation of cross-sectional surveys of children in the United States from 1971 to 1994.3 National data were collected from 5 surveys conducted in 1963 to 1965 (National Health Examination Survey II), 1966 to 1970 (National Health Examination Survey III), 1971 to 1974 (National Health and Nutrition Examination Survey I), 1976 to 1980 (National Health and Nutrition Examination Survey II), and 1988 to 1994 (National Health and Nutrition Examination Survey III).3

Globally, growth charts are typically used to monitor growth and overall infant health and nutritional status. A critical period for growth and development is from birth to 2 years. Presently, there are at least 2 charts available, and they differ, which may cause confusion.

These primary data sets were supplemented by data collected by vital statistics units at the federal level, at the State of Wisconsin, the State of Missouri Vital Statistics, the Fels Longitudinal Study, and the Pediatric Nutrition Surveillance System (82,382,522 infants included for weight-for-age chart; 911,723 infants included for

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length-for-age chart).3 Data from both breast-fed and formula-fed infants were included in these data sets, the data were statistically weighted, and the percentile charts were ‘‘smoothed,’’ but data from very low-birth-weight infants (ie, those less than 1,500 g) were excluded.3 In addition, data for infants of different races were combined. The WHO 2006 growth charts were developed to address the recognized shortcomings of the CDC 2000 growth charts and to create a prescriptive, rather than a descriptive, approach to defining normal growth. The WHO growth charts (birth to 24 months) are based on data collected longitudinally from 6 centers during 1997 to 2003.4 The construction of the growth charts was developed using growth data of infants enrolled in the WHO longitudinal study from varying ethnic and cultural backgrounds in 6 countries (Brazil, United States, India, Norway, Ghana, and Oman) (27,853 infants included for weight-for-age chart; 27,334 infants included for length-for-age chart; 26,985 infants included for body mass index [BMI]Yfor-age chart).5 The percentile charts were smoothed percentiles. Infants assessed were born at term gestation, were exclusively or predominantly breast-fed between 4 and 6 months, and were partially breast-fed up to 1 year after the introduction of complementary foods at 4 to 6 months.4Y7 Similar to the CDC charts, the data for infants of different races were combined. The CDC and American Academy of Pediatrics have recently considered the adoption of the WHO 2006 growth charts for application in the United States.8 The data collection was tightly controlled, and the homogeneity of the infant-feeding characteristics was strictly maintained in constructing the WHO 2006 growth charts. However, only limited analyses9 have been performed to assess the impact of the use of these new charts if they were implemented for monitoring growth in US and/or Canadian infants. A major limitation in performing such analyses has been the lack of large cohorts of infants for whom longitudinal growth data have been tracked prospectively.

The CDC and American Academy of Pediatrics are considering the adoption of the WHO 2006 growth charts for application in the United States, but a final decision has not been made.

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The CDC 2000 growth charts are currently used as a growth reference in the United States and Canada. The CDC 2000 growth charts are derived from data from a mixed-feeding population (ie, both breast-fed and formula-fed). These data were collected from a series of descriptive, cross-sectional studies with a large composite sample size. Researchers have questioned whether the CDC charts are appropriate to use for monitoring the growth of breast-fed infants, because the population used to establish the CDC charts included some infants fed infant formula exclusively.10,11 Conversely, there are concerns about using the WHO growth charts to monitor the growth of formula-fed infants. Thus, there is a need to assess how breast-fed infants track on the CDC charts and how formula-fed infants track on the WHO charts, as both charts are widely used. The WHO 2006 growth charts include BMI charts for infants from birth to 2 years. Body mass index is globally used as a reference to classify weight status in older children and adults, but its use in infants has not yet been considered for implementation in the United States and/ or Canada. The usefulness of the WHO BMI charts in infants needs to be established. To do so, an appropriate cohort of infants representative of those used to establish the curves needs to be plotted on the BMI charts. Because the WHO 2006 BMI charts comprised exclusively or predominantly breast-fed infants, we chose to compare BMI patterns of a breast-fed cohort to these BMI charts. The objectives of our study were (1) to compare and contrast the CDC 2000 and WHO 2006 growth charts, (2) to compare the growth patterns of US and Canadian breast-fed and formula-fed infants on the CDC 2000 and WHO 2006 growth charts, and (3) to describe the BMI indices for a cohort of US and Canadian breast-fed infants when plotted on the WHO 2006 BMI charts.

Evaluation Methods Population Studied Breast-fed Infants The cohort of healthy, term breast-fed infants used for this analysis was the reference group in a study conducted from 1997 to 2000 to measure the growth and mental development of preterm infants.12 The term (38Y42 weeks) breast-fed infants were exclusively or predominantly breast-fed (similar to the inclusion criteria for the WHO longitudinal study subjects)5 for 4 months or longer. Weight and length at birth were obtained from birth records. These infants were followed up prospectively, and their weights and lengths were measured at 1, 2, 3, 4, 6, 9, 12, and 18 months of age at 15 study sites across the United States and 1 site in Canada. Study participants were weighed Nutrition Today, Volume 42



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without clothing or diapers on a calibrated pediatric scale. Length was measured in the recumbent position using a standard pediatric apparatus. Of the 105 infants enrolled in this study, 95 infants were American, and 10 were Canadian. Formula-fed Infants Healthy, term formula-fed infants used for this analysis participated in a trial from 1995 to 1996 that measured the effect of docosahexaenoic acidY and arachidonic acidYsupplemented formula on growth, visual acuity, and mental development.13 Formula-fed cohort A comprised infants fed a standard infant formula (Enfamil with iron, Mead Johnson & Co, Evansville, Ind). Formula-fed cohort B comprised infants fed another standard infant formula (Enfamil LIPIL with iron, Mead Johnson & Co). Weight and length at birth were retrieved from birth records. These infants were followed up prospectively, and their weights and lengths were measured at 2 weeks, and at 2, 4, 6, 9, and 12 months of age at 13 investigator sites across the United States and 1 site in Canada. Subjects were weighed without clothing or diaper on a calibrated pediatric scale. Length was measured in the recumbent position using a standard pediatric apparatus. Of the 127 infants enrolled in the formula-fed cohort A, 107 were American, and 20 infants were Canadian. Of the 134 infants enrolled in the formula-fed cohort B, 115 were American, and 19 were Canadian.

Growth Charts Growth percentiles for the CDC 2000 and WHO 2006 growth charts were obtained from the Web sites, http:// www.CDC.gov/growthcharts and http://www.WHO.int/ childgrowth/standards/en/, respectively. The longitudinal measurements for the 3 cohorts of infants were then plotted on the CDC 2000 and WHO 2006 growth charts. In addition, the breast-fed cohort was plotted on the WHO 2006 BMI chart. The interpretation and comparative analysis of these cohorts were based on the plotted values.

Comparison of Weight and Length Growth Charts The WHO and CDC curves for male and female infants are presented in this report to demonstrate the major outcomes of our analyses. When superimposed, the weight-for-age growth charts (published by the CDC in 2000 and WHO in 2006) show different growth trajectories for the 5th, 50th, and 95th percentiles from birth to approximately 18 months of age (see Figures 1 and 2). The 50th percentiles for the CDC 2000 and WHO 2006 weight growth charts intersect twice in the first 6 months. The CDC 2000 curve tracks above the WHO 2006 curve until approximately 1 month. Thereafter, it

Figure 1. Weight for ageVmales. CDC 5th, 50th (heavy solid line), and 95th percentiles curves and WHO 5th, 50th (heavy dashed line), and 95th percentile curves. Nutrition Today, Volume 42



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Growth of US and Canadian Infants

Figure 2. Weight for ageVfemales. CDC 5th, 50th (heavy solid line), and 95th percentile curves and WHO 5th, 50th (heavy dashed line), and 95th percentile curves.

tracks below the WHO 2006 curve until approximately 6 months. After 6 months, the CDC 2000 curve remains above the WHO 2006 curve through approximately 3

years of age, at which time the curves converge (not shown). In contrast to differences in weight, the length-for-age 50th percentile curves for male and

Figure 3. Length for ageVmales. CDC 5th, 50th (heavy solid line), and 95th percentile curves and WHO 5th, 50th (heavy dashed line), and 95th percentile curves. 154

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Figure 4. Length for ageVfemales. CDC 5th, 50th (heavy solid line), and 95th percentile curves and WHO 5th, 50th (heavy dashed line), and 95th percentile curves.

female infants from the CDC 2000 and WHO 2006 growth charts appear to be similar from birth to 18 months of age (see Figures 3 and 4).

When superimposed, the WHO and CDC weight-for-age growth charts show different growth trajectories for the 5th, 50th, and 95th percentiles out to approximately 18 months of age.

Breast-fed and Formula-fed Cohorts Compared Figures 5 and 6 display the weight-for-age growth curves for male infants for the 2 formula-fed cohorts during the first 12 months and the breast-fed cohort to 18 months of age plotted with the CDC 2000 and the WHO 2006 weight percentiles, respectively. The breast-fed cohort and the 2 formula-fed cohorts show similar weight Nutrition Today, Volume 42



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growth patterns through 12 months of age. When plotted on the CDC 2000 weight reference chart (see Figure 5), the infants from all 3 cohorts grow above the 50th percentile from 2 to 6 months. After 6 months, the weights of the formula-fed cohorts track along the 50th percentile until 12 months, whereas the weights of the breast-fed cohort track along the 50th percentile until 18 months of age. When the same data are plotted on the WHO 2006 weight reference chart (see Figure 6), all 3 cohorts track along the 50th percentile until approximately 6 months. Thereafter, the weights of the cohorts track above the 50th percentile and approach the 75th percentile at approximately 12 months of age. The weights of the formula-fed cohorts reach the 75th percentile at about 12 months, whereas those of the breast-fed cohort reach the 75th percentile at approximately 16 months of age. The length growth patterns for the breast-fed cohort track similarly on the CDC 2000 and WHO 2006 length reference charts, that is, above the 50th percentile until 18 months of age (data not shown). The length growth patterns for the formula-fed cohorts track above the 50th percentile on the CDC 2000 length reference chart, whereas the same cohorts track along the 50th percentile on the WHO 2006 length reference chart until 12 months of age (data not shown).

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Breast-fed Cohort Plotted on Body Mass Index Chart Figure 7 shows the cohort of male breast-fed infants plotted for the first 18 months of life on the WHO BMI 2006 reference percentiles. The cohort appears to track along the 50th percentile for the first 6 months. Thereafter, the breast-fed cohort tracks above the 50th percentile and reaches the 75th percentile at approximately 16 months of age.

WHO and CDC charts differ in weight for age, but are similar in length for age.

Discussion Our evaluation shows that there are differences between the CDC 2000 and WHO 2006 growth charts for weight, whereas the length charts are similar. The differences between the 2 weight charts result in differences in the number of US and Canadian infants identified at the

Growth of US and Canadian Infants

various percentiles, regardless of the mode of feeding. Our findings for US and Canadian infants are similar to those reported in other countries.14 The authors of this other study did not report specific feeding practices of their infants, which limits the ability to interpret the effect of feeding regimen. The current study specifically addressed the issue of feeding mode. The CDC 2000 growth charts are representative of American infants who were fed mixed diets (ie, breast-fed and formula-fed), using data collected 2 to 4 decades ago. Therefore, the CDC 2000 growth charts are not reflective of the growth of an exclusively breast-fed population. Plotting the growth of breast-fed infants on these charts may lead to misinterpretation by those who are not aware of the differences in the growth of breast-and bottle-fed infants. The WHO 2006 growth charts differ from the CDC charts, as they provide a prescriptive approach to defining normal growth.4Y7 The WHO 2006 growth charts provide a global representation of a homogeneously fed group of infants. However, the WHO charts lack representation of formula-fed or mixed-fed infants and include data from only those who adhered to a stringent feeding protocol that may vary from current US and/or Canadian feeding practices. The differences in the 2 growth charts for weight percentiles are most pronounced during the first 2 years of life. Infants are seen frequently during the

Figure 5. Weight for age plotted on the CDC 2000 weight reference chartVbreast-fed (asterisk with solid line) and formula-fed (cohort A, open diamond with dashed line; and cohort B, open square with dashed line) male infants. 156

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Figure 6. Weight for age plotted on the WHO 2006 weight reference chartVbreast-fed (asterisk with solid line) and formula-fed (cohort A, open diamond with dashed line; and cohort B, open square with dashed line) male infants. first 2 years of life for well-baby examinations and immunizations, whereas visits after 2 years are often limited to acute illnesses. Thus, the differences in these 2 growth charts may have their greatest impact on how healthcare professionals perceive an individual infant’s growth during the first 2 years of life. Practitioners need to be mindful that classification of their patients into percentiles will depend on which chart is used. The WHO weight charts will result in a higher percentile classification compared with the CDC weight charts, as described by our study and that of others.11 Weights for age of the cohorts of breast-fed and formula-fed infants presented here were similar. When plotted on the WHO 2006 weight chart, all 3 cohorts tracked from the 50th to 75th percentiles by about 12 months, while these cohorts track closely to the 50th percentile on the CDC chart. One explanation for this observation is that the WHO 2006 growth charts do not accurately reflect the growth of US and/or Canadian infants during the first 12 months of life. An alternative explanation is that US and/or Canadian feeding practices are different than those of their global counterparts. In any event, more research is needed to clarify this. Yet another explanation for the differences in weight curves for US and Canadian infants plotted on CDC 2000 and WHO 2006 growth charts beyond about 6 months of Nutrition Today, Volume 42



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life is that feeding management varies considerably between US and/or Canadian infants and their global counterparts regardless of mode of early infant feeding. Specifically, the weaning period and the introduction of complementary feeding occur around this time period and may vary considerably among different countries. If this is the case, one could speculate that more emphasis should be placed on dietary management of the older infant, that is, beyond 6 months. Some evidence supports this view. For example, the Feeding Infant and Toddler Study15 data suggest that US infant and toddler dietary patterns are concerning, with parents reporting low intakes of fruits and vegetables and a high consumption of sweetened beverages, salty snacks, and desserts.15 However, the Feeding Infant and Toddler Study report was a descriptive analysis based on 24-hour dietary recalls and telephone interviews lacking longitudinal and prospective assessment of continuing complementary feeding patterns.15 Despite the limitations of the Feeding Infant and Toddler Study data, it is, to date, the only published study evaluating current dietary intake patterns in a large population of US infants and toddlers. There is a need for greater understanding of the dietary practices and management of the vulnerable age group of later infancy and toddlerhood. The studies we analyzed were conducted during an analogous time frame (late 1990s) to one another, at

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Growth of US and Canadian Infants

Figure 7. BMI plotted on the WHO BMI 2006 reference percentilesVbreast-fed male infants. multiple sites, and with similar inclusion and exclusion criteria except for the mode of feeding. Because the objective of our analysis was to compare the 2 growth charts and not the cohorts, the inclusion of cohorts from different studies is not considered to be a serious limitation. A limitation was that information regarding complementary feeding was not available for either the breast-fed or formula-fed cohorts. Therefore, we cannot be certain as to when and how complementary feeding was managed. Despite these limitations, these data provide a serial assessment of growth of a number of US and Canadian infants with diverse ethnicity and geographical locations. An unexpected finding was that our cohort of breast-fed infants reached the 75th percentile by approximately 16 months on the WHO 2006 BMI chart. Although it is correlated with percentage body fat, many nutritionists recognize that BMI fails to distinguish between increased mass in the form of fat, lean tissue, or bone16Y21; hence, BMI has limitations for directly assessing adiposity.16,17,19,22 Despite these concerns about the use of BMI, Nader et al23 have recently shown that children achieving a greater number of BMI values at or above the 75th percentile at any age over 2 years have an increased risk of being overweight in early adolescence. When the weight and BMI data for the US and Canadian breast-fed infants shown in this analysis and 158

Nader’s data are considered collectively, we conclude that there is a need for additional prospective studies to clarify the role diet plays in both early and late infancy in influencing the risk for obesity in later childhood or adulthood. There is also a need to validate the use of the WHO 2006 BMI charts in identifying infants at risk for overweight and/or obesity.19,22Y24

Conclusions In summary, there are differences in the growth trajectories of the CDC 2000 and the WHO 2006 growth charts for weight. If the WHO 2006 growth charts are adopted for use in the United States and/or Canada, healthcare professionals need to be aware that the classification of infants at risk for overweight and/or obesity may change. This change may alter clinical decisions about the management of pediatric patients among those who are not aware of the subtleties between the charts. Pediatricians and other health professionals need education and guidance on how to interpret and evaluate information gathered from plotting infants on the WHO growth charts versus those of the CDC. Perhaps expert bodies, such as the American Academy of Pediatrics and CDC, could lead the way in providing such direction to the pediatric community. Nutrition Today, Volume 42



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Acknowledgment This study was sponsored by Mead Johnson Nutritionals. Paul W. Ferguson, PhD, received his PhD in animal breeding and genetics from Ohio State University. He is currently the associate director of Clinical Research at Mead Johnson Nutritionals. Susan Hazels Mitmesser, PhD, received her PhD in Nutritional Biochemistry from the University of Nebraska. She is currently the manager of Global Medical Communications at Mead Johnson Nutritionals. Nirvarthi Maharaj, MD, received her MD from the University of Witswatersrand in Johannesburg, South Africa. Dr Maharaj did a medical internship at Mead Johnson Nutritionals in 2006. Carol Lynn Berseth, MD, received her MD from the University of Pittsburgh School of Medicine. She is currently the director of Medical Affairs North America at Mead Johnson Nutritionals. Corresponding author: Susan Hazels Mitmesser, PhD, Mead Johnson Nutritionals, 2400 W Lloyd Expressway, Evansville, IN 47721 (e-mail: [email protected]).

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