BMC Pediatrics

BioMed Central

Technical advanceOpen AccessA new growth chart for preterm babies: Babson and Benda's chart
updated with recent data and a new format
Tanis R Fenton*
Address: Department of Community Health Sciences, Faculty of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, T2N
4N1, Canada
Email: Tanis R Fenton* - tanisfenton@shaw.ca* Corresponding author

Published: 16 December 2003
BMC Pediatrics 2003, 3:13

Received: 10 June 2003
Accepted: 16 December 2003

This article is available from: http://www.biomedcentral.com/1471-2431/3/13© 2003 Fenton; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media
for any purpose, provided this notice is preserved along with the article's original URL.

Abstract
Background: The Babson and Benda 1976 "fetal-infant growth graph" for preterm infants is
commonly used in neonatal intensive care. Its limits include the small sample size which provides
low confidence in the extremes of the data, the 26 weeks start and the 500 gram graph increments.
The purpose of this study was to develop an updated growth chart beginning at 22 weeks based ona meta-analysis of published reference studies.
Methods: The literature was searched from 1980 to 2002 for more recent data to complete the
pre and post term sections of the chart. Data were selected from population studies with large
sample sizes. Comparisons were made between the new chart and the Babson and Benda graph.
To validate the growth chart the growth results from the National Institute of Child Health andHuman Development Neonatal Research Network (NICHD) were superimposed on the newchart.
Results: The new data produced curves that generally followed patterns similar to the old growthgraph. Mean differences between the curves of the two charts reached statistical significance afterterm. Babson's 10th percentiles fell between the new data percentiles: the 5th to 17th for weight,
the 5th and 15th for head circumference, and the 6th and 16th for length. The growth patterns of
the NICHD infants deviated away from the curves of the chart in the first weeks after birth. Whenthe infants reached an average weight of 2 kilograms, those with a birthweight in the range of 700
to 1000 grams had achieved greater than the 10th percentile on average for head growth, but
remained below the 3rd percentile for weight and length.
Conclusion: The updated growth chart allows a comparison of an infant's growth first with thefetus as early as 22 weeks and then with the term infant to 10 weeks. Comparison of the size of
the NICHD infants at a weight of 2 kilograms provides evidence that on average preterm infants
are growth retarded with respect to weight and length while their head size has caught up to birth
percentiles. As with all meta-analyses, the validity of this growth chart is limited by theheterogeneity of the data sources. Further validation is needed to illustrate the growth patterns ofpreterm infants to older ages.

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Background
Growth monitoring is a part of the medical and nutritional assessment of preterm infants. Growth charts provide the basis for this assessment by providing acomparison to a reference which allows for a visual picture of both the infant's achieved size and growth trajectory. Parents and health professionals like to knowwhether a preterm infant is able to maintain growth velocity or achieve catch-up in growth compared to the fetus
and the term infant. Intrauterine growth charts allow thiscomparison for infants before term. Babson and Benda(Babson) [1] extended an intrauterine chart past term age
by including a section based on the growth of infants bornat term. They published this chart in 1976 which theyreferred to as a "fetal-infant growth graph".
The growth chart developed by Babson is still recommended for use in Neonatal Intensive Care Units [2,3]. In
a recent survey of 118 neonatal health professionals, thegrowth chart used most frequently was that of Babson [1](50%), followed by that of Lubchenco, Hansman &, Boyd[4] (42%) and then by the one by Dancis [5] (18%)(unpublished data).
Although commonly used, Babson's growth chart has limitations. The X axis begins at 26 weeks of gestation thus
limiting its usefulness to plot younger preterm infants
from birth. The Y axis is made in 500 gram increments
which make precise plotting difficult. The sample size ofthe data behind Babson's chart was small. There were only
45 infants in their sample that were 30 weeks or younger[6]. The data was 15 years old at the time of publicationand is now 40 years old.
The purpose of this project was to prepare an updated
fetal-infant Babson-type growth chart for use in neonatal
intensive care units. This chart will allow a comparison forpreterm infants as young as 22 weeks of gestation, firstwith intrauterine and then with post term references.

Methods
Literature review and selection
A search of the literature was conducted on three databases (Pub Med, the Cochrane Library, EMBASE from1980 to June 2002) using the subject headings: infant,(premature, very low birthweight), anthropometry,
growth, birthweight, head, cephalometry, gestational age,newborn, and reference values. Articles selected included
surveys of intrauterine and post term growth. Reference
lists of relevant articles were searched.

To improve on the Babson graph, two types of data wereneeded: infant size measured at the time of birth for the
intrauterine section and term infant measurements for the
post-term section. Population studies with large sample

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sizes were preferred to improve generalizability. The
World Health Organization has recommended that gestational age of infants be described as completed weeks [7],so data stated in this manner were favored. Numerical
data were preferred over graphic depiction to ensure
accuracy.
Intrauterine data
Three recent large population based [8-10] surveys ofbirthweight for various gestational ages were identified in
the literature search. These studies used statistical methods to delete implausible birth weight-gestational age
combinations and then smoothed the birth weight curves
across gestational age categories. The Canadian study by
Kramer et al [8] was selected for the intrauterine weightsection since their methods produced the most plausible
distribution of birth weights particularly for 28 through36 weeks. For example, the 50th and 90th percentiles for 32
weeks in Alexander's corrected data were 2.2 and 3.2 kilograms (kg) respectively. The 50th and 90th percentiles for
32 weeks in Kramer's corrected data were the more plausible 1.9 and 2.3 kg, respectively. Kramer et al used a statistical method to correct for misclassification of term
infants incorrectly labeled as preterm. Table 1 lists details
regarding the data sources used.

Two population based studies that met the a priori criteria
included head circumference and length, one from Sweden by Niklasson et al [11] and one from Australia by
Beeby et al [12]. A limitation with the Swedish survey wasthat it did not include data prior to 29 weeks, however
both were used since the Swedish study was based on alarge sample.
To develop the head circumference and length curves, thenumerical data from Niklasson [11] and Beeby [12] wereaveraged together using a weighted average based on total
sample size. Ideally the combining of these two data
sources would have been done with the raw data to create
one distribution for each gestational age, however thiswas not possible from the published data. Since the sample sizes were very different (380,000 vs 30,000), theresulting weighted averages were predominantly influenced by the Swedish data. Therefore the head circumference and length curves are only Australian data prior to 30
weeks and then predominately Swedish data after 30
weeks.
There was remarkable consistency between the head andlength results from the Australian and Swedish studies.
Between 31 and 33 weeks; the differences were less than
0.3 centimeter (cm) for 50th percentiles and 0.4 cm for the
10th and 90th percentile curves. The magnitudes of the differences were greater for data at 29 weeks and greater than
36 weeks which may to be due to the way the Swedish

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Table 1: Details of the Data Sources
Kramer [8]Niklasson [11]Beeby [12]

CDC [13]

Data used

Birthweight ≤ 40 weeks

Head and length measures ≤ 40 weeks

Sample size (n)676,605

376,000

Head and length measures ≤ 40
weeks
Head circumference: 29090 andlength: 26973

n < 30 weeks
Gestational age range ofstudy
Inclusion criteria
Exclusion criteria

4101
22 to 43 weeks

0
28.5 to 42.5 weeks

274
22 to 43 weeks

Weight, head and length
measures after term
Birth data :weight: 82 million,
length: 900,000, headcircumference: 400. First yearof life: 2200 to 38,000 infants.
N/A
Post term

All births
Ontario (province) was
excluded due to problems withdata quality.

"Healthy" newborn infants
Stillbirths, twins, complications during
pregnancy with potential effects on
fetal growth and significant
malformations
1977 to 81
yesSingleton livebirths
Multiple births

NHANES surveys
Infants with birthweights <1500 grams

1982 to 1995
yes

Primarily 1963 to 1994
N/A

In the majority of cases thegestational age was based on firsttrimester ultrasound, or when earlyultrasound was not available, last
menstrual period dates were used.
In < 1% of cases, the Ballard
assessment was used when neither
dates nor ultrasound were available.
The mother's medical record was
examined and following verificationof the gestational age and other data,
outliers were either accepted as realor corrected.

N/A

Dates
Completed gestational
weeks
Method to assessgestational age

1994 to 1996
yes

Outliers

Assumed a log normal
distribution of birthweight ateach gestational age andcompared the probabilities ofaccurate versus misclassificationof infant's gestational age.

"early ultrasound has
increasingly been the basis forgestational age assessments inrecent years"

Last menstrual period was used when
it was in agreement (+/- 2 weeks) withthe obstetric assessment. If not, thelatter was used. When either estimate
was missing the gestational age wasconsidered unknown.

data was reported. These data were expressed as a third
degree polynomial function, so their curves were curved
downward at both ends. At the ends of the curves the differences increased to 0.4 cm at both ends of the curve forhead circumference and to 0.8 cm (29 weeks) and 1.0 cm(40 weeks) for length. (This problem was dealt with under
Smoothing of the Curves.) The consistency in the mid sections of the curves provides confidence regarding the combining of the results from these two studies.
Post 40 week data
In selecting the term infant data for the post 40 weeks section of the fetal-infant chart the Center for Disease Control (CDC) [13-15] data met the a priori criteria of being
based on large samples and having a numerical version
available. The CDC Growth Data is a compilation of
growth surveys of American multiracial-ethnic breast andformula fed infants born between 1963 and 1994 [13].
The data are mostly cross sectional, but include some longitudinal measures.
Chart development
The data for both genders were averaged together for the
3rd, 10th, 50th, 90th and 97th percentiles to create one
growth chart. Separate gender charts were not produced
since the gender differences were considered not important enough to warrant separate charts. The sample sizes
for the birthweight data are very large, so significant differ-

Curves were smoothed witha variety of parametric andnon-parametric procedures

ences between the genders could be seen for most ages
even when the differences were small and of minor practical importance. Specifically, the differences between themale and female weights were statistically significant at allages above 23 weeks for the 50th percentile (beginningwith a difference of 32 grams) and above 24 weeks for the
3rd percentile (beginning with a difference of 44 grams).
None of the head and length or the CDC data werereported in a manner that permitted a statistical comparison by gender.
The largest differences between the genders were confinedto late gestation and after term. Along the 3rd percentile,
there was only one weight difference between the genders
that was greater than 100 grams (40 weeks) and none of
the head differences were greater than 0.4 cm. The differences between the genders along the 10th percentile werelimited to greater than 36 weeks for weight differences
greater than 100 grams and only 1 head difference wasgreater than 0.6 cm. Along the 50th percentile the only differences between the genders for weight more than 100
grams were greater than 35 weeks and the only head differences greater than 0.4 cm were after term. For each ofthese three percentiles, only 1 length measure was greaterthan 1 cm and all of these were after term.
A large-scale grid was used to aid accuracy of plotting. The
increments were 100 grams for weight, one cm for head

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circumference and length, and one-week intervals fortime. The chart was extended to 50 weeks since the majority of preterm infants are discharged home by this age.
Spaces were made at the bottom of the chart to note thedate of measurements. The 3rd, 10th, 50th, 90th and 97th
percentile curves for weight, head circumference andlength were plotted on the grid. There were disjunctions
between the data sets at 40 weeks. For example, the CDC
50th percentile for weight was 2% lower than the Kramer
value, while the 3rd percentile was 14% lower. The disjunctions between the pre and post-term sections arelikely due to artifacts of the original data sets and theprocessing methods.
Smoothing of curves
To produce a working chart, the disjunctions between the
pre and post term sections needed to be smoothed. It wasdifficult to merge the pre- and post-term data sets at theirboundaries. The goal of the smoothing was to produce a
bridge between the pre-term and the post-term curves
without the typical deceleration seen in intrauterine
curves just before term. Initial approaches to numericallysmooth the boundary produced obvious undesirable
results. Therefore manual methods were used to smooththe disjunction from the deceleration point of the preterm curves to a point prior to the first measurement after
term (at 2 months).

For weight the smoothing was done between 36 and 46
weeks. (Figure 1) The 50th percentile needed the least
modifying since both the Kramer and CDC weights at
term were approximately 3.5 kg. The 3rd percentile
required smoothing up to 49 weeks. The smoothing forhead circumference and length was continued back to 22
weeks to level the disjunction between the two data
sources at 29 weeks. All of the curves had merged with the
CDC curves prior to 50 weeks.

FigureIllustrationdata
curves1 of smoothed curves superimposed on the raw
Illustration of smoothed curves superimposed on the raw
data curves. Solid curves are from the original data, dottedcurves are the smoothed and final version.

The final curves (Figure 2) were illustrated with different
graphic styles to identify the different percentiles.
Comparisons with the Babson chartThree comparisons were made between Babson's chartand the new data. First, a graphical comparison was prepared of Babson's mean, 3rd and 97th percentiles superimposed on the new raw data (Figure 3). Second, means
were compared between Babson's and the raw data basedon the assumption that the data was not skewed, andtherefore the 50th percentiles were equal to the mean. This
comparison was done using t-test at 28, 30, 32, 36, 40
weeks and 1.5 and 2.5 months. Standard deviations were
estimated using a least squares fit of the percentiles to thenormal curve. It was not possible to test for differences
prior to 28 weeks since Babson did not include percentile
curves until 28 weeks. A probability of p < 0.05 was con-sidered statistically significant and adjustment was madefor multiple comparisons using the Bonferroni method.
The 10th percentile is a frequent cut point for assessmentof size for age. The third comparison was a calculation of
the percent of new chart values below Babson's 10th percentile. This was done by first calculating Babson's 10th
percentile using the standard deviation estimate. Then zscores were calculated for Babson's 10th percentile compared to the new distributions and an estimate was madeof the percent of new data below Babson's 10th percentile.
This comparison was done at 28, 30, 32, 36 and 40 weeks
and at 1 and 2 months.

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FigureA
new fetal-infant
2
growth chart for preterm infants developed through a meta-analysis of published reference studies
A new fetal-infant growth chart for preterm infants developed through a meta-analysis of published reference studies.

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FigureThe
growthdottedcurves
3 curves
superimposed
are Babsonon
andtheBenda's
raw data
1976
curvesfetal-infant
The dotted curves are Babson and Benda's 1976 fetal-infant
growth curves superimposed on the raw data curves.

How does the growth of preterm infants appear on thechart?
The data from the large multicenter cohort study done by
the National Institute of Child Health and Human Development Neonatal Research Network (NICHD) [16] weresuperimposed on the new growth chart (Figure 4). This
study documented the growth patterns of 1660 very low
birthweight infants born in 1994 and 1995. Infants withanomalies and those that did not survive were excluded
from the study, but those with a variety of morbidities
were included. For this comparison, the growth trends ofthe infants of average birthweights 550, 750, 950 and
1450 were used.

Results
Comparisons with the Babson chart
The graphical comparison of Babson's mean, 3rd and 97th
percentiles [1] superimposed on the new raw data showedsimilar values along the 50th percentile (Figure 3) withgreater differences for the 3rd and 97th percentiles.

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FigureThe
National
Neonatal
postnatal
4InstituteResearch
growthofNetworkChilddata ofHealth4superimposedof theandinfantHumancohorts
onDevelopment
the new
fromcharttheThe postnatal growth data of 4 of the infant cohorts from the
National Institute of Child Health and Human Development
Neonatal Research Network superimposed on the newchart.

When the means of Babson's and the new data were compared, head circumference and length measures were significantly different (p < 0.00005) after term. The small
numbers in the sample used by Babson [6] before term
limited the power of the statistical comparison to find differences for the younger ages. The largest numerical differences in mean weight between the two sources were at 36
weeks where the new data was 120 grams higher and at
2.5 months where the new data was 143 grams lower. The
largest differences in means for head circumference andlength were 1.0 centimetre at 1.5 months and 1.2 cm at 26
weeks, respectively. The largest discrepancies for all 3
parameters were at the 97th percentile, with differences forweight of 260 grams at 36 weeks, for head circumferenceof 1.1 cm at 32 weeks and for length of 1.8 cm at both 30
and 32 weeks.
The percent of values below Babson's 10th percentile
ranged from the 5th to 17th for weight, the 5th and 15th

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for head circumference, and the 6th and 16th for length(data not shown).
How does the growth of preterm infants appear on thechart?
The growth curves from the NICHD for weight, length andhead circumference showed clear deviations away fromthe intrauterine curves in the first weeks after birth. (Figure 4) The subsequent growth in weight of the infants
with birthweights less than 1 kilogram was less than thelate intrauterine rate but steeper than the post term slope.
When the infants reached an average weight of 2 kilograms, all of the average weight growth curves were below
the 10th percentile, and the smaller three groups remained
below the 3rd percentile. The average growth of head circumference recovered the original birth percentiles except
for the smallest group. Only the smallest group's averagehead size remained below the 10th percentile. The average
growth in length also recovered from the post birth deceleration but like weight, only the largest group had an average size above the 3rd percentile.

Discussion
This new fetal-infant chart is an updated Babson-type
growth chart for use in neonatal intensive care units. This
chart will allow a comparison for preterm infants as
young as 22 weeks of gestation first with intrauterine andthen with post term references and it can replace the one
developed by Babson [1] which has been used in neonatal
intensive care for over 25 years. The 10th percentile of thischart is accurate to the source data prior to 36 weeks;
therefore it could be used for the assessment of size for
gestational age for infants smaller than 2 kilograms.
This meta-analysis does not represent the actual growth ofpreterm infants for three reasons. First, the initial parts ofthe curves are based on the size of fetuses at birth, which
do not show the change in weight that occurs after birth.
This is followed by curves based on the growth of term
infants who have not had the growth depressing effect ofprematurity [17]. Another approach for monitoring
growth of preterm infants using growth charts is to use alongitudinal postnatal growth chart. These growth chartsshow the pattern of initial weight loss after birth followedby subsequent growth of a sample of preterm infants.
Examples include those by Dancis et al [5], Wright et al[18], and those developed by the Infant Health Development Program [19], and by the NICHD [16]. These longitudinal charts have the advantage of using samples of very
low birth weight infants as the growth reference andshowing the actual growth pattern of preterm infants.
Their disadvantage is that they are not based on thegrowth standard for preterm infants, that is, on fetal
growth [20,21]. Therefore they do not show an infant's
growth velocity or catch-up in growth relative to the fetus

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or the term infant. Further, the curves on a longitudinal
growth chart are highly influenced by the medical andnutritional care of the sample infants; growth patterns
may change with innovations in medical and nutritionalcare [22]. The use of both fetal-infant and longitudinal
charts together provide a more accurate assessment ofgrowth of preterm infants [22].
Second, the validity of a meta-analysis is affected by methodological quality of the individual studies and the extent
of heterogeneity in the studies and their results. Data fromdifferent studies were combined to prepare the graphs. It
would have been preferable if all the data could have beenobtained from one study with uniform methodology. Thea priori criteria did limit the studies to those that were
population based, had large sample sizes, and recorded
gestational age in completed weeks. The studies used were
all from developed countries where the majority ofwomen are well nourished and the three studies used forthe preterm section have publicly funded universal healthcare. The studies have slight differences in the inclusionand exclusion criteria (Table 1) which could have influenced their results. The most notable differences between
the studies were the exclusion of multiple births from theSwedish and Australian surveys and the statistical adjustment of the Canadian survey data. There is evidence thatthe birthweight of infants from multiple gestations are
reduced relative to the weight of singletons after 28 to 30
weeks of gestation [23]. The consistency of the results ofthe two sources of head circumference and length data
was remarkable, which suggests that the differences
between these two studies were not substantial.
Could a secular trend make the combining of the data
invalid? There has been a slight trend towards an increasein birthweight of term infants in the United States and in
Canada of 1 to 3 grams per year on average over the timeframe that the data were collected [24,25]. No trends areapparent among infants of lower gestational ages [24,25].
Regarding head and length size, there is some evidence ofsmall increases over this time period [26]. Since these differences are slight, their influence on the data is not likelyof clinical significance.
Third, the smoothing that was applied to bridge the preand post term curves may or may not be a valid estimateof the growth of preterm infants. Further validation studies will determine the soundness of the smoothed disjunction between the data sets. The ideal validation study
would compare the growth of a population of healthy preterm infants followed prospectively from birth though 50
weeks post-conceptual age. Healthy infants should be
used to decrease the chance of bias due to illness of prematurity, however it would be useful to also document
the growth patterns of unwell infants on this growth chart.

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The superimposed NICHD growth curves (Figure 4) represent a mixed group of infants, some without complications and others with morbidities, and with varying sizefor gestational age [16]. When the infants from this study
approached the average weight of 2 kilograms thoseinfants with a birthweight in the range of 700 to 1000
grams on average achieved the 10th percentile for head
growth, but remained below the 3rd percentile for weight
and length.
This finding is similar to that seen in previous studies of
the growth of preterm infants on this type of growth
chart[16,17,27]. The growth of most preterm infants plotted on this type of chart track lower curves or below the
curves because of the initial weight loss after birth and theextended time required for catch up growth to occur[17,28]. There appears to be a priority among preterm
infants for growth of head circumference over weight andlength growth [27] and of weight over length growth[17,27]. Catch up growth of preterm infants is a long term
process and small preterm infants are growth retarded
during the first years of life [17]. The curves of the fetalinfant growth chart provide a backdrop against which an
infant's growth trajectory can be plotted.
There were agreements and differences between thisnewer data with that of Babson. The agreements suggestthat the Babson curves had fairly accurate depictions ofinfant size which may account for the continued popularity of this chart. The differences may reflect the small sample sizes of the early chart and the use of only maternal
dates for the gestational age [6]. The larger sample sizes
used here may provide better confidence in the extreme
percentiles [29].
The fetal-infant chart encourages the use of age that is
adjusted for prematurity after 40 weeks. Once an infantsurpasses 50 weeks, the regular CDC growth charts could
be used, with continued adjustment for prematurity.
Some authors have suggested that age be adjusted forpreterm infants to at least 3 years [30], or even up to 7
years [31].
The data behind the new chart are predominantly crosssectional. Data of this type can be criticized since they arebased on attained size of individuals and not on actual
growth patterns [15]. However, cross sectional growth
charts, such as the CDC Growth Charts, are useful forassessment of growth over time [15].
The selection of the CDC data for the post 40 week section
may not be ideal since the database excluded preterm
infants with a birth weight less than 1.5 kg. These infants
grow differently than those of higher birthweight and thisexclusion make the CDC charts more like a growth stand-

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ard [14]. However, this data of mostly normal birthweight
infants have some advantages in that they are intuitively
understood and their use aids the assessment of whether
catch-up growth is occurring. As well, for those infants
that may cross percentiles upward, the CDC curves of
infants born at term provide a guide for a realistic
expected size for age and what size is heavier than
expected. An additional advantage from using the CDC
data is that after 50 weeks of post menstrial age atransition can be made from the chart developed here to
the CDC charts.
It has been suggested that the distribution of weights
among fetuses that are born preterm may be smaller thanthose that remain in utero and are delivered at term [32],and therefore it may be better to use ultrasound data formeasures of the size of infants that are not born prematurely. There are two reasons why it may be desirable tocontinue to use the size of preterm infants at birth as a
growth reference. First, ultrasound data are variable andlack reproducibility [32-34]. As well, measurement of preterm infants provides weight, head circumference andlength measurements while ultrasound only provides estimates of these measures.
The use of growth charts is only as accurate as the measurements that are made of the infants. Measurements ofweight on electronic scales [35] and head circumference
using paper tapes [36] have been shown to be reliable.
However, measurement of length, even under controlled
conditions on clinically stable infants is not very accurateor reliable and therefore growth may be undetected orappear excessive or inadequate [37]. To improve accuracyof length data, infants should be measured on a headboard by two people [38].
Unfortunately the literature that accompanied the population based data sources does not include a description of
the scales and tapes used to measure the infants, nor of theaccuracy of these instruments. Since the data sources were
population based, it is likely that a variety of precisionoccurred.
Head growth is important to monitor, since growth thatdeviates from the intrauterine rate could indicate problems [39,40]. Calculation of growth velocity (gram/kg/
day over several days) is recommended since it is a precise
measure of growth [38]. The most comprehensive growthassessment uses a calculation of growth velocity together
with assessment of size relative to references for a given
age on a growth chart.
At term age, infants born prematurely tend to have a different body composition than infants born at term, withlower weight, lean tissue and bone mineral content and a

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higher percent body fat [41]. The optimum bodycomposition of the growing preterm infant is not known
nor easily measured. Current growth charts provide noassessment of body composition.

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2.
3.
4.

Conclusions
This updated fetal-infant chart supports growth monitoring of preterm infants from as early as 22 weeks gestational age to 10 weeks post term age. It allows acomparison of an infant's growth with first the fetus andthen the term infant and therefore allows an evaluation ofcatch up growth. Although Babson's "fetal-infant growthgraph" had reasonably accurate estimates along the 50th
percentile, the larger sample sizes and more accurate gestational age assignments used here may provide better
confidence in the extreme percentiles. As with all metaanalyses, the validity of this growth chart is affected by themethodological quality of the data sources and the heterogeneity of their results.

5.
6.

7.
8.

9.
10.

Comparison of the growth of the NICHD infants at
attained weight of 2 kilograms provides evidence that, on
average, preterm infants are growth retarded with respect
to weight and length while, except for the smallest infants,
their average head size has caught up to birth percentiles.
Further validation work is needed to illustrate the growth
patterns of preterm infants to older ages.

11.

List of Abbreviations

14.

12.
13.

kilogram (kg)centimeter (cm)
15.

Center for Disease Control (CDC)
National Institute of Child Health and Human Development Neonatal Research Network (NICHD)

Competing interests

16.

17.

None declared.

Authors' contributions
TF carried out the literature search, data selection, griddesign, chart development, statistical comparisons andmanuscript preparation.

18.
19.

Acknowledgements

20.

Thanks to: Pat Fenton for assistance with the computer graph preparations,
Doug McMillan for scientific and editorial advice, Debbie McNeil for statistical advice and Sari Czink and Suzanne Tough for editorial assistance.

21.

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