Reference Population: Standard Normal Curve

Reference Population: Standard Normal Curve

95th5th

50th Percentile

Indicators of Nutritional StatusIndicators of Nutritional Status

<5th percentileStunting/shortness length or height-for-age

Head circumference-for-age

<5th percentile

<5th percentile>95th percentile

Underweight weight-for-length BMI-for-age

Indicators of Nutritional StatusIndicators of Nutritional Status

Overweight Weight-for-length BMI-for-age

>95th percentile

Risk of overweight BMI-for-age

85th to 95th percentile

Reference Data Sets: Birth to 36 Months Reference Data Sets: Birth to 36 Months

Weight-for-Length

Weight

Length

Head Circum

MO/WI Natality National Natality PedNSS

Fels NHANES III ('88-'94) NHANES II ('76-'79)

NHANES I ('71-'74)

B 3 6 9 12 15 18 21 24 27 30 33 36 Age in Months

Reference Data Sets: 2 to 20 Years Reference Data Sets: 2 to 20 Years

Weight/BMI

Stature

NHANES III ('88-'94) NHANES II ('76-'79) NHANES I ('71-'74)

HES III ('66-'70) HES II ('63-'65)

2 4 6 8 10 12 14 16 18 20

Age in Years

Exclusions from the Reference DataExclusions from the Reference Data

• VLBW infants (<1500 g) were excluded because they have different growth patterns

• NHANES III weight data for 6+ year olds were excluded to avoid an upward shift in weight and BMI-for-age curves

• VLBW infants (<1500 g) were excluded because they have different growth patterns

• NHANES III weight data for 6+ year olds were excluded to avoid an upward shift in weight and BMI-for-age curves

*>95th percentile BMI-for-age 1 Troiano et al, Arch Pediatr Adolesc Med 1995: 149: 1085-1091.*>95th percentile BMI-for-age 1 Troiano et al, Arch Pediatr Adolesc Med 1995: 149: 1085-1091.

Age-Adjusted Prevalence of Overweight* From NHANES I to III1

Age-Adjusted Prevalence of Overweight* From NHANES I to III1

0

5

10

15

20

Boys 6-11 y Boys 12-17 y Girls 6-11 y Girls 12-17 y

NHANES I I I I I I

Sex and Age GroupSex and Age Group

Perc

en

tP

erc

en

t

CDC Growth Charts Are for All Racial and Ethnic Groups Combined

CDC Growth Charts Are for All Racial and Ethnic Groups Combined

• The effect of race and ethnicity on growth is controversial

• Inadequate sample data for racial- and ethnic- specific charts

• Environmental influences appear to contribute to variations in growth but more research is needed

Age Adjusted Prevalence of Low Height-for-Age by Ethnic Groups, Children Aged 0 to 5 Years1

Age Adjusted Prevalence of Low Height-for-Age by Ethnic Groups, Children Aged 0 to 5 Years1

0

5

10

15

79 80 81 82 83 84 85 86 87 88 89 90 91 92 93

WhiteAsian

Year of Visit Year of Visit

Perc

en

tag

e

1 Yip and Mei, 1995

Breast-Fed vs. Formula-Fed Infants Breast-Fed vs. Formula-Fed Infants

• Mode of infant feeding can influence growth

• New charts represent the combined growth patterns of breast-fed and formula-fed infants

• Separate charts are not recommended

• Working group of the World Health Organization (WHO) is collecting data on infants following the WHO feeding recommendations to develop charts for infants and children through age 5.

• Mode of infant feeding can influence growth

• New charts represent the combined growth patterns of breast-fed and formula-fed infants

• Separate charts are not recommended

• Working group of the World Health Organization (WHO) is collecting data on infants following the WHO feeding recommendations to develop charts for infants and children through age 5.

Disjunction: Smoothed in New ChartsDisjunction: Smoothed in New Charts

40

50

60

70

80

90

100

110

120

0 6 12 18 24 30 36 42 48 54 60Age in month

Len

gth

/heig

ht

in c

m

40

50

60

70

80

90

100

110

120

0 6 12 18 24 30 36 42 48 54 60Age in month

Len

gth

/heig

ht

in c

m

Old New

• Racially and ethnically diverse

• Birth to 36 months: nationally representative

• Breast-fed and formula-fed infants

• Racially and ethnically diverse

• Birth to 36 months: nationally representative

• Breast-fed and formula-fed infants

Reference Population for CDC Growth Charts

Reference Population for CDC Growth Charts

New Reference Curves Compared with Old Curves*

Prevalence of Nutrition Indicators

New Reference Curves Compared with Old Curves*

Prevalence of Nutrition IndicatorsBirth to 36 Months

Nutrition Indicator Change in Prevalence

Stunting/shortnesslength-for-age <5th

2% to 4% lower from 6-24 mos

Underweightweight-for-length <5th

* NHANES III, PedNSS, WHO

Overweightweight-for-length >95th

Same

3% to 5% higher

New Reference Curves Compared with Old Curves*

Prevalence of Nutrition Indicators

New Reference Curves Compared with Old Curves*

Prevalence of Nutrition IndicatorsChildren 2 to 5 years of age

Nutrition Indicator Change in Prevalence

Stunting/shortnessheight-for-age <5

2% to 3% lower

Underweight** <5 3% to 5% higher

* NHANES III, PedNSS, WHO**BMI-for-age, weight-for-stature

Overweight** 95th 3% to 5% higher

Charts extend to 20 years

3rd and 97th percentiles available

Lower limits of length (45 vs. 49 cm) and height (77 vs. 90 cm) extended

BMI-for-age charts (2-20 years) added

85th percentile (at risk of overweight) added

Charts extend to 20 years

3rd and 97th percentiles available

Lower limits of length (45 vs. 49 cm) and height (77 vs. 90 cm) extended

BMI-for-age charts (2-20 years) added

85th percentile (at risk of overweight) added

New in the CDC Growth ChartsNew in the CDC Growth Charts

What Is BMI?What Is BMI?

• Body mass index (BMI) = weight (kg)/height (m)2

• BMI is an effective screening tool; it is not a diagnostic tool

• For children, BMI is age and gender specific, so BMI-for-age is the measure used

• Body mass index (BMI) = weight (kg)/height (m)2

• BMI is an effective screening tool; it is not a diagnostic tool

• For children, BMI is age and gender specific, so BMI-for-age is the measure used

Advantages of BMI-for-AgeAdvantages of BMI-for-Age

Provides a reference for adolescents that was not previously available

Consistent with adult standards so can be used continuously from2 years of age to adulthood

Tracks childhood overweight into adulthood

Provides a reference for adolescents that was not previously available

Consistent with adult standards so can be used continuously from2 years of age to adulthood

Tracks childhood overweight into adulthood

Tracking BMI-for-Age from Birth to 18 Years with Percent of Overweight Children who Are Obese at Age

251

16 15 12 11 10 917 19

55

7567

26

52

69

8377

36

0

20

40

60

80

100

Birth 1 to 3 3 to 6 6 to 10 10 to 15 15 to 18

Age of child (years)

% o

be

se

as a

du

lts

BMI < 85th BMI >=85th BMI >=95th

Whitaker et al. NEJM: 1997;337:869-873

Advantages of BMI-for-AgeAdvantages of BMI-for-Age

BMI-for-age relates to health risks

Correlates with clinical risk factors for cardiovascular disease including hyperlipidemia, elevated insulin, and high blood pressure

BMI-for-age during pubescence is related to lipid levels and high blood pressure in middle age

BMI-for-age relates to health risks

Correlates with clinical risk factors for cardiovascular disease including hyperlipidemia, elevated insulin, and high blood pressure

BMI-for-age during pubescence is related to lipid levels and high blood pressure in middle age

• Weight-for-stature measurements

• Measures of body fat

BMI-for-Age Compares Well with

Why Use BMI-for-Age?Why Use BMI-for-Age?

• Recommended by expert committees to evaluate overweight

• Recommended by expert committees to evaluate overweight

Guidelines for Overweight in Adolescent Preventive

Services (Am J Clin Nutr 1994;59:307-316) Obesity Evaluation and Treatment: Expert Committee Recommendations (Pediatrics 1998 Sept;(102)3:e 29) Assessment of Childhood and Adolescent Obesity: International Obesity Task Force (Am J Clin Nutr 1999, 70,suppl)

Shape of Growth Curves: Weight-for-Stature versus

BMI-for-Age

Shape of Growth Curves: Weight-for-Stature versus

BMI-for-Age

10

15

20

25

30

35

24 72 120 168 216

Age (months)B

MI

0

5

10

15

20

25

30

35

80 90 100 110 120 130

Stature (cm)

Wei

gh

t (k

g)

95th

50th

5th

95th

50th

5th

Example: 95th Percentile Tracking Age BMI

2 yrs 19.3 4 yrs 17.8 9 yrs 21.013 yrs 25.1

For Children, BMI Differs by Age

Boys: 2 to 20 years

BMI BMI

BMI BMI

Shape of BMI-for-Age Growth Curve: “Adiposity” Rebound (AR)

Example: Early AR

Age (mos) BMI 26 18.2 32 17.4 38 18.5 41 18.7

Boys: 2 to 20 years

BMI BMI

BMIBMI

BMI

BMI-for-Age CutoffsBMI-for-Age Cutoffs

> 95th percentile Overweight

85th to < 95th Risk of overweight percentile

< 5th percentile Underweight

• Using the 85th and 95th percentiles as cut points, few children are incorrectly identified as over-fat but some over-fat children will be missed.

• It is desirable to correctly identify those children not at risk of overweight or overweight.

• Using the 85th and 95th percentiles as cut points, few children are incorrectly identified as over-fat but some over-fat children will be missed.

• It is desirable to correctly identify those children not at risk of overweight or overweight.

Performance of BMI-for-Age as a

Screening Tool

Can you see risk?

• This boy is 3 years, 3 weeks old.

• Is his BMI-for-age

- below the 5th percentile? - 5th to <85th percentile: normal? - >85th to <95th percentile: at risk for overweight? - >95th percentile: overweight?

Photo from UC Berkeley Longitudinal Study, 1973

Measurements:

Age=3 y 3 wks

Height=100.8 cm (39.7

in)

Weight=18.6 kg (41 lb)

BMI=18.3

BMI-for-age= >95th

percentile overweight

Plotted BMI-for-Age

Boys: 2 to 20 years

BMI BMI

BMI BMI

Can you see risk?

• This girl is 4 years, 4 weeks old.

• Is her BMI-for-age

- below the 5th percentile? - 5th to <85th percentile: normal? - >85th to <95th percentile: at

risk for overweight? - >95th percentile: overweight? Photo from UC Berkeley Longitudinal Study,

1974

Measurements:

Plotted BMI-for-Age

Girls: 2 to 20 years

Age= 4 y 4 wks

Height=106.4 cm (41.9 in)

Weight=15.7 kg (34.5 lb)

BMI=13.9

BMI-for-age= 10th percentile Normal

BMI BMI

BMIBMI

Can you see risk?

• This girl is 4 years old.• Is her BMI-for-age

- below the 5th percentile?- 5th to <85th percentile: normal?- >85th to <95th percentile: at

risk for overweight?- >95th percentile: overweight?

Photo from UC Berkeley Longitudinal Study, 1973

Measurements: Age=4 y

Height=99.2 cm (39.2 in)

Weight=17.55 kg (38.6 lb)

BMI=17.8

BMI-for-age= 94thpercentile

At risk for

overweight

Plotted BMI-for-Age

Girls: 2 to 20 years

BMI

BMIBMI

BMI

5 1/2 year old boy

Weight: 41.5 lb

Height: 43 in

BMI= 15.8

BMI-for-age=50th %tile

Inaccurate height measurement: 42.25

BMI=16.3

BMI-for-age=75th %tile

Accurate Measurements are Critical

Boys: 2 to 20 years

BMI BMI

BMI BMI

Summary of Using BMI-for-Age

• BMI-for-age is the recommended method for screening overweight and underweight

• For children, BMI is age and gender specific; for adults there are fixed

cut points

• Accurate and periodic measurements are important elements of any anthropometric screening

Available CDC Growth ChartsAvailable CDC Growth Charts

• Birth to 36 months

Weight-for-length

Length-for-age

Weight-for-age

Head circumference-for-age

• Birth to 36 months

Weight-for-length

Length-for-age

Weight-for-age

Head circumference-for-age

Available CDC Growth ChartsAvailable CDC Growth Charts

• 2 to 20 years

BMI-for-age

Stature-for-age

Weight-for-age

Weight-for-height

• 2 to 20 years

BMI-for-age

Stature-for-age

Weight-for-age

Weight-for-height

Steps to Plot BMI-for-AgeSteps to Plot BMI-for-Age

• Select appropriate growth chart• Record data• Obtain accurate weight and

height measurements• Calculate BMI• Plot measurements• Interpret plotted measurements

• Select appropriate growth chart• Record data• Obtain accurate weight and

height measurements• Calculate BMI• Plot measurements• Interpret plotted measurements

Case Study: “Sam” Case Study: “Sam”

• Name: Sam• Weight: 37 lb 4 oz (16.9 kg)• Height: 41.5 inches (105 cm)• DOB (date of birth): 9/15/1994• DOV (date of visit): 4/4/1998

• Name: Sam• Weight: 37 lb 4 oz (16.9 kg)• Height: 41.5 inches (105 cm)• DOB (date of birth): 9/15/1994• DOV (date of visit): 4/4/1998

Data Entry Table for BMI-for-AgeData Entry Table for BMI-for-Age

Mother’s Height________Father’s Height________

Age

4/4/98

GestationalAge________ Weeks

Weight

37 lb 4 oz

CommentDate Height BMI

41.5 in

Formula: weight (kg)/[height (m)]2

Calculation: [weight (kg)/ height (cm)/

height (cm)] x 10,000

Formula: weight (kg)/[height (m)]2

Calculation: [weight (kg)/ height (cm)/

height (cm)] x 10,000

Calculating BMI with the Metric System

Calculating BMI with the Metric System

Example: A child’s weight=16.9 kg and height=105.4 cm

BMI = [16.9 kg / 105.4 cm / 105.4 cm] x 10,000 = 15.2

Calculating BMI with the English SystemCalculating BMI with the English System

Formula: weight (lb)/[height (in)]2 x 703

Calculation: [weight (lb)/height (in)/height (in)] x 703

Formula: weight (lb)/[height (in)]2 x 703

Calculation: [weight (lb)/height (in)/height (in)] x 703

Example: A child’s weight = 37 pounds, 4 ounces and height = 41 1/2 inches

(convert fractions to decimal value)

BMI = [37.25 lb / 41.5 in / 41.5 in] x 703 = 15.2

Data Entry Table for BMI-for-AgeData Entry Table for BMI-for-Age

Mother’s Height________Father’s Height________

Age

3 1/24/4/98

GestationalAge________ Weeks

Weight

37 lb 4 oz

Comment

15.2

Date Height BMI

41.5 in

Sam’s BMI Plotted on Boy’s BMI-for-Age Chart

Sam’s BMI Plotted on Boy’s BMI-for-Age Chart

Interpretation:

• Sam’s BMI-for-age is slightly below the 25th %tile so it falls within the normal range.

• Of 100 boys who are the same age, fewer than 25 have a BMI-for-age lower than Sam’s.

Boys: 2 to 20 years

BMI BMI

BMI BMI

BMI-for-Age CutoffsBMI-for-Age Cutoffs

> 95th percentile Overweight

85th to < 95th Risk of overweight percentile

< 5th percentile Underweight

Interpreting the BMI-for-Age Chart Interpreting the BMI-for-Age Chart

• BMI-for-age indicates a child’s weight in relation to his/her height for a specific age and gender

• Need a series of BMI plots to

determine the growth trend

• If indices deviate from normal growth patterns, further assessment may be needed

• BMI-for-age indicates a child’s weight in relation to his/her height for a specific age and gender

• Need a series of BMI plots to

determine the growth trend

• If indices deviate from normal growth patterns, further assessment may be needed

Future Directions for CDC Training

• Continuation of training at national meetings

• Development of a Web-based training module

• Training focus: accurate weighing and measuring, calculating BMI, plotting and interpreting the growth charts

Distribution of CDC Growth Charts

Electronic Copies

http://www.cdc.gov/growthcharts/