Volume 11 Issue 1 (February) - Australasian Society for Ultrasound ...

Australian charts for assessing fetal growth – a review
Fig.2: Hadlock's chart.
Fig.1: Beeby's population based birthweight percentile chart.
newborn infants’ growth characteristics correctly.
One of the first published population-based charts was
produced in Western Australian in 1989 by Kliewer, et al. 14 .
They extracted data from the WA Midwives’ Notification
System, which recorded details of all births of 20 weeks gestation
or more, or birthweight of 400 g or more from 1980
to 1986. Gestational age was calculated from last menstrual
period. The charts were not specifically designed to act
as standards of intrauterine growth, but to compare health
outcomes between indigenous and non-indigenous babies.
They found that the distributions of both birthweight and
gestational age were shifted downward in Indigenous infants
compared with white infants, a trend that unfortunately
persists today. These charts were also gender-specific, with
separate charts for male and female babies, recognising the
importance of sex on fetal size.
In 1996, Beeby published the first NSW population-based
birthweight percentile charts, which was also the largest
Australian population-based study at the time. This study
included data from 422 139 live born singletons held by the
NSW Midwives Data Collection and from King George V
Hospital 15 . Separate charts for male and female infants were
developed. The charts followed the general trend of increasing
birthweights over time and had generally higher percentiles
than previously published charts.
The first Australian birthweight percentiles published
using national data were published in 1999 by Roberts and
Lancaster 16 . They aimed to develop national birthweight
percentiles by gestational age (GA) for male and female
singleton infants and then to compare BW distributions by
GA for indigenous and non-indigenous infants. Using data
from the National Perinatal Statistics Unit (NPSU), 761 902
births were analysed and birthweight percentiles for indigenous
and non-indigenous Australian-born women were
made. They included only singleton live infants delivered
by Australian-born mothers in the non-indigenous charts
in order to reduce environmental factors associated with
migrant populations. In keeping with the WA data, indigenous
infants were more likely to be classified as SGA and
preterm than non-indigenous infants. More specifically,
Fig.3: Customised chart.
birthweights of indigenous infants diverged from that of the
non-indigenous population after 34 weeks. By 40 weeks,
the median birthweight for male indigenous babies was 160 g
below that of non-indigenous males and birthweight for
female indigenous infants was 130 g below non-indigenous
females. More than 17% of indigenous infants born at term
were classified as SGA. Separate charts for indigenous
births were published, but the authors cautioned that they
should not be interpreted as separate population norms until
the effect of population and environmental differences could
be ascertained.
While the authors acknowledged that birthweight percentiles
do not necessarily represent fetal growth standards,
the 10th centile on these charts are the current standard used
by the NPSU for defining fetal growth restriction in the perinatal
mortality data collection system.
Advantages of birthweight charts
n Standards can be derived from very large numbers and
are therefore statistically robust;
n Population-based data provides a more demographically
representative sample to be obtained compared with hospital
or private practice populations;
ASUM Ultrasound Bulletin 2008 February 11 (1)