Jornal de Pediatria - Vol. 78, Nº3, 2002 219
0021-7557/02/78-03/219
Jornal de Pediatria
Copyright © 2002 by Sociedade Brasileira de Pediatria
ORIGINAL ARTICLE
Weight/length ratio: is it a good index to assess
the nutritional status of full-term newborns?
Taciana D. de A. Braga,1 Marília C. Lima2
Abstract
Objective: an accurate assessment of the nutritional status of an infant at birth is very important, since
it provides information on early identification of pathological events related to intrauterine growth
acceleration or retardation. Anthropometric ratios such as weight/length and mid-arm circumference/head
circumference may be used as alternative tools for this purpose. The main objective of this study was to
verify the correlation between triceps skinfold thickness with Rohrer Index, Body Mass Index, weight/
length ratio, and mid-arm circumference/head circumference ratio.
Methods: a cross-sectional study was carried out with 390 full-term newborns delivered at the
Maternity Ward of Instituto Materno Infantil of Pernambuco, from May to July 1999. The newborns had
their birthweight, length, head and mid-arm circumferences and triceps skinfold thickness measured.
Results: the results showed that among the anthropometric indices studied the weight/length ratio
showed the strongest correlation with triceps skinfold thickness (r = 0.63, P< 0.001) followed by mid-arm
circumference/head circumference ratio ( r = 0.59, P< 0.001). Rohrer index showed the weakest correlation
(r = 0.43, P< 0.001). Multiple linear regression analyses revealed that weight/length ratio correlated best
with skinfold thickness.
Conclusions: we concluded that among the studied indices, weight/length ratio showed to be the best
alternative to assess the nutritional status of infants at birth.
J Pediatr (Rio J) 2002; 78 (3): 219-24: itrauterine growth, anthropometric indices, skinfold thickness,
nutritional assessment, weight/length ratio, mid-arm circumference/head circumference ratio.
Introdução
Nutritional assessment in the neonatal period reflects
the average growth pattern from conception to birth. It
serves as a basis for future assessments and helps to identify
infants who are at risk for perinatal complications associated
with abnormal fetal growth. Since the 1960’s, the nutritional
status of newborns has been classified according to the
duration of the gestation period and their birthweight, based
on the study conducted by Battaglia & Lubchenco,1 as small
for gestational age (SGA), appropriate for gestational (AGA)
age and big for gestational age (BGA). This criterion is
purely statistical, ignoring the individual growth potential
and reflecting only the total body mass for a given gestational
age; in other words, it does not indicate how this body mass
1. Master’s degree in Pediatrics from Universidade Federal de Pernambuco.
Neonatologist of Instituto Materno-Infantil de Pernambuco.
2. PhD, Associate Professor, Universidade Federal de Pernambuco.
Manuscript received Oct 29 2001. Accepted for publication Mar 13 2002.
219
220 Jornal de Pediatria - Vol. 78, Nº3, 2002
is distributed over the linear surface. The drawbacks of
using a single criterion to assess the nutritional status at
birth have led researchers to consider the use of
anthropometric indicators and skinfold measurement as an
alternative to a more precise method. The most frequently
studied indicators are those that result from the relationship
between weight and height (Rohrer index, body mass index,
weight-for-height ratio) and also between arm circumference
and head circumference.2-8
In fact, there is no agreement on which the best way to
assess nutritional status at birth should be. The impact of
early detection of intrauterine growth disorders will only be
perceived when an appropriate criterion is routinely applied.
Although nutritional anthropometry in the neonatal
period is largely discussed by researchers, we verify that
there is little information about it or little interest in learning
about its importance and interpretation. Since the currently
used criteria are limited, it is necessary to find an indicator
(or indicators) for the postnatal assessment of intrauterine
growth quality that is reliable, easy to use and easy to
calculate.
The present study aimed at assessing Rohrer index (PI),
body mass index (BMI), weight for height (W/H) ratio and
arm circumference/head circumference (AC/HC) ratio as
indicators of the nutritional status of full-term newborns,
identifying which of them better correlates with subcutaneous
fat mass.
Methods
A descriptive, cross-sectional study was carried out at
the Instituto Materno-Infantil de Pernambuco (IMIP), from
May to July 1999. The IMIP is a non-governmental,
privately-owned, non-profit organization, located in the
city of Recife, which assists the population who seeks
medical care at the Unified Health System. The institute is
a statewide reference center for high-risk pregnancies. The
sample consisted of 390 full-term newborns, result of a
single pregnancy, either delivered naturally or by C-section.
The study comprised newborns with evident signs of
congenital infections, chromosomal anomalies and
malformations.
The sample size was calculated using the Sample Power
1.0 software from the Statistical Package for the Social
Sciences (SPSS), version 8.0. The value of 0.50 was
considered to be the lowest acceptable correlation coefficient
for a good predictor between skinfold measurement and
anthropometric indicators, while 0.60 was the expected
correlation coefficient for the population. These values
were based on the study conducted by Yau & Chang.3 By
considering an alpha error of 5% and a beta error of 20%,
the sample size necessary to identify the lowest correlation
coefficient with statistical significance would be 383
newborns.
Weight/length ratio: is it a good index... - Braga TDA et alii
A pilot study was carried out in the last two weeks of
April 1999 with the aim of inspecting the equipment and
testing the research protocol. The weight assessment
technique was checked by the on-duty staff of the maternity
ward, and the scales was inspected by INMETRO (Brazilian
Institute of Metrology and Industrial Quality). The
techniques used for anthropometric assessment were those
recommended by Gibson.9 The following criteria were
used: birthweight was checked in the first hour of life by the
on-duty staff (doctors, resident doctors or medical students)
at the neonatal unit or by the main researcher, when present
during delivery. The height, head circumference, arm
circumference and triceps skinfold were evaluated by the
main researcher within the first 24 hours of life, taking into
consideration the highest value of three consecutive measures
for head circumference, the mean value of three consecutive
measures for arm length and circumference, and the mean
value of two consecutive measures for triceps skinfold. If
the two skinfold measures had a difference greater than
0.3mm, a third measure was performed, and the mean of the
two nearest values was considered. The compression time
for measuring skinfold was 15 seconds. Arm circumference
and triceps skinfold measurements were performed on the
left arm, at the midpoint between the acromion and olecranon.
The following measurement devices were used: electronic
scales (Filizola, model BP no. 620/95), with a 15-kg capacity,
dismountable anthropometer with fixed scale, fiberglass
measuring tape and Harpenden caliper, with a constant
pressure of 10g/mm² and an accuracy of 0.2 mm. The
anthropometric measurements were limited to five per shift
so that their quality could be maintained. The gestational
age was estimated by clinical evaluation within the first 24
hours of life by the method devised by Capurro et al.10
After anthropometric measurement, the values for the
following anthropometric indicators were obtained: Rohrer
index (weight/height³ x 100), body mass index (weight/
height²), weight-for-height ratio, and arm circumference/
head circumference ratio.
For the quality control of data, an assessment of the
intraobserver variation for anthropometric indicators (height,
head circumference, arm circumference, and triceps
skinfold) was made using the technical error of measurement
(TEM) and the reliability coefficient (R),11 in a subsample,
which represented 10% of the total number of analyzed
newborns.
The present measurements showed a technical error of
measurement less than 0.1, and a 99% intraobserver
reliability for arm circumference, 97% for head
circumference, 96% for height measurements, and 91% for
triceps skinfold.
The EPI-Info version 6.04 was used for the processing
and preliminary analyses of data. The consistency of double
data entry was checked by the Validate subprogram. Initially,
the distribution symmetry of anthropometric indicators was
assessed by the histogram. Afterwards, the degree of
Weight/length ratio: is it a good index... - Braga TDA et alii
Jornal de Pediatria - Vol. 78, Nº3, 2002 221
association between the triceps skinfold and anthropometric
indicators was evaluated by Pearson correlation coefficient.
The dispersion diagram (on Excel) was used for the graphical
representation of the correlation between anthropometric
indicators, using the triceps skinfold as dependent variable.
A multiple linear regression analysis was performed with
SPSS version 8.0, by the stepwise method, in order to
determine which of the analyzed anthropometric indicators
is the best predictor for triceps skinfold. The statistical
significance level was established at 0.05.
After verbal agreement, the patients’ mothers signed an
informed consent form, allowing their infants to participate
in the study. The research project was approved by the
Ethics and Research Committee of the Center for Health
Sciences of Universidade Federal de Pernambuco.
Results
Among the 390 evaluated newborns, 197 (50.5%) were
males and 193 (49.5%) were females. The mean gestational
age was 39 weeks (SD 2.0).
We observed that the triceps skinfold had a statistically
significant correlation with all the analyzed indicators, of
which the weight-for-height ratio had the best correlation
coefficient, followed by the arm circumference/head
circumference ratio. Rohrer index was the one that best
correlated with the triceps skinfold (Table 1 and Figures 1
to 4). The results of the multivariate linear regression
analysis presented in Table 2 show that only the weight-forheight ratio and the arm circumference/head circumference
ratio significantly contributed towards the prediction of
triceps skinfold fat mass. In this case, the weight-for-height
Table 1 -
ratio was the best predictor. The body mass index and the
ponderal index lost their statistical significance in the
multivariate analysis, yielding P values of 0.29 and 0.33,
respectively.
Discussion
Anthropometric indicators show body proportion and
have been proposed as an alternative to improve the accuracy
of the nutritional status assessment of newborns. In general,
most authors found a good correlation between the variation
of predictive values of these indicators and perinatal
morbidity and mortality.3,4,12-16
Figure 1 - Dispersion of triceps skinfold thickness and weight/
lenght ratio (W/L) in full-term newborns, IMIP 1999
Correlation coefficient between the anthropometric indices and the triceps skinfold
thickness in 390 full-term newborns - IMIP, 1999
Anthropometic indices
r
CI 95%
Statistical analysis
Weight/lenght ratio
0.63
(0.56 - 0.68)
P< 0.001
Arm circumference/
head circumference ratio
0.59
(0.52 - 0.65)
P< 0.001
Body mass index
0.58
(0.50 - 0.64)
P< 0.001
Rohrer index
0.43
(0.34 - 0.50)
P< 0.001
r = Pearson’s correlation coefficient.
222 Jornal de Pediatria - Vol. 78, Nº3, 2002
Weight/length ratio: is it a good index... - Braga TDA et alii
Table 2 -
Multiple linear regression of the anthropometric indices
and the triceps skinfold thickness in 390 full-term
newborns- IMIP, 1999
Indices
B
CI 95%
R²
P
Weight/lenght ratio
0.04
0.03 - 0.05
Arm circumference/
head circumference ratio
12.69
8.37 - 16.99 0.44 < 0.001
0.39 < 0.001
B = non-standard regression coefficient.
R² = determination coefficient.
Figure 2 - Dispersion of triceps skinfold thickness and arm
circumference/head circumference (AC/HC) ratio in
full-term newborns, IMIP - 1999
Skin fat mass is early affected by changes in nutritional
status, increasing or decreasing its contents, since its
mobilization is an important source of calories. Triceps
skinfold measurements have greater values in BGA
newborns, if compared to AGA newborns, and can help
distinguish actually malnourished newborns from those
whose body constitution is naturally small.17,18
Figure 4 - Dispersion of triceps skinfold thickness and Rohrer
index (RI) in full-term newborns, IMIP - 1999
By analyzing the correlation between the anthropometric
indicators discussed here and the triceps skinfold, we
attempted to find the indicator that could better define
nutritional status at birth. These anthropometric indicators
can be easily obtained and simply performed, and are part
of the routine physical examination of newborns, except for
the arm circumference measurement.
Most studies on anthropometric indicators as a way to
define nutritional status in the neonatal period are related to
Rohrer index, which has been increasingly used on newborns,
and to the arm circumference/head circumference ratio.
The association of these indicators with gestational age,
birthweight, and neonatal morbidity and mortality has been
largely studied. Few studies assess the correlation of these
indicators with subcutaneous fat mass.3,19
Figure 3 - Dispersion of triceps skinfold thickness and body
mass index (BMI) in full-term newborns, IMIP 1999
Among the four indicators discussed here, the simple
correlation between weight and height proved to be the best
correlation coefficient with subcutaneous fat mass (r= 0.63;
Weight/length ratio: is it a good index... - Braga TDA et alii
P <0.001), which is in conformity with studies carried out
in China and in Israel.3,19 The same occurred with the
multiple linear regression analysis.
The order of the correlation degree of anthropometric
indicators in the present study coincides with that observed
in the studies mentioned above. Rohrer index had the lowest
correlation coefficient with subcutaneous fat mass, whether
it is correlated with the skinfold of one or several body sites.
It was also observed that, between the indicators that relate
weight and height, the correlation coefficient decreases as
the height is squared in the body mass index, and as it is
cubed in Rohrer index, thus confirming the observations of
some authors that question the use of these indicators,
especially Rohrer index, since, if the height is cubed, an
indicator that is extremely prone to measurement failures is
validated.
The significant correlation between the analyzed
indicators and subcutaneous fat mass showed that the use of
these indicators can improve the accuracy of nutritional
assessment of newborns. However, the use of Rohrer index
should be questioned, since it had the lowest correlation
coefficient with subcutaneous fat mass (r= 0.43; P <0.001),
and also because its calculation is hard to be used in clinical
practice. On the other hand, we observed that the arm
circumference/head circumference ratio, after the weight
for height ratio, was the indicator that presented the best
correlation coefficient with skinfold measurement; however,
its routine use implies introducing one more indicator into
physical examination since arm circumference is not part of
the assessment of newborns.
The weight-for-height ratio can play an important role in
the assessment of nutritional status in newborns, since it is
easy to calculate, results from simple indicators whose
assessment are part of the daily routine, and because it had
the best correlation with subcutaneous fat mass in this
study.
We should not forget that the use of this indicator or any
other indicator as a way to determine neonatal nutritional
status requires that normal cutoff points be known. According
to Abramson,20 normality can be defined in several ways:
as something usual, based on statistical criteria, or as a
desirable situation, a standard to be achieved or, still, a state
that requires no intervention. In general, the statistical
criterion is used; however, we believe that prospective
studies that follow the evolution of newborns in the medium
and long run can be more appropriate to establish these
cutoff points.
We conclude that, among the analyzed anthropometric
indicators (PI, BMI, W/H, AC/HC), the indicator resulting
from the simple relationship between weight-for-height
(W/H) was the one that best correlated with triceps skinfold,
proving to be a good alternative to nutritional assessment at
birth.
Jornal de Pediatria - Vol. 78, Nº3, 2002 223
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Weight/length ratio: is it a good index... - Braga TDA et alii
Correspondence:
Dra. Taciana Duque de Almeida Braga
Rua Setúbal 1630/401
CEP 51130-010 – Recife, PE, Brazil
Telephone: +55 81 91372205
E-mail: [email protected]