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Chapter Five
Ultrasound Prediction of At Risk Birth Weight in Chinese and Caucasian Fetuses
in Normal Pregnancy and those Complicated by Gestational Diabetes Mellitus
5.1
Introduction
Gestational diabetes mellitus (GDM) is defined as a glucose intolerance of any level with
onset or first diagnosis during pregnancy. Pregnant women at the Royal North Shore and
Hornsby Ku-Ring-Gai Hospitals in Northern Sydney undergo a 50g glucose challenge
test (GCT) at 28 weeks gestation and those with a level > 7.8mm/l proceed to a 75g
glucose tolerance test (GTT), where a positive diagnosis of GDM is made if 2 of the 3
levels are increased (Fasting >5.2mm/l, 1hr >9.9mm/l, 2hr >8.5mm/l). The aim of
management with GDM is to keep glucose levels in normal range with a combination of
moderate exercise, diet and/or insulin therapy. If glucose levels are poorly controlled it
can result in increased fetal growth and a higher risk incidence of macrosomia (birth
weight > 4000 grams) with associated birth complications. Ultrasonic fetal monitoring is
appropriate if the pregnancy is complicated by poor glucose control, hypertension, large
for gestational age or intra uterine growth restriction.
In Australia around 3% of
Caucasian pregnancies are affected by GDM compared with up to 15% in Asians
(Fulcher et al 1998). In Chapter Four it was demonstrated that in an Australian Chinese
population problems associated with birth weight and macrosomia occur when the birth
weight is over 3,500 grams compared with 4000 grams in the Caucasian population. In
this group of Chinese women it was found that there was a high level of obstetric
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intervention (60%) and a 20% incidence of post partum haemorrhage and concluded that
there was a failure to recognise the at risk Chinese fetus due to applying Caucasian
standards. Homko et al (1995) assessed the interrelationship between gestational diabetes
mellitus, ethnicity and fetal macrosomia, concluding that the ethnic variation seen in fetal
growth may be as a result of genetic factors and influences of different in-utero growth
promoters in those populations. Sabbagha (1976), Parker (1981), Hadlock et al (1990)
and Arenson (1995) have written on the plausibility of racially specific growth charts,
with the general consensus being that it is not necessary to differentiate between the
groups because, even though there may be a difference in birth weights due to ethnicity,
there is a similar rate of growth during the last trimester. Spencer et al (1995) thought it
was inappropriate to use standard charts for abdominal circumference and estimated fetal
weight charts for Asian women due to their lower body mass index as the stature of the
mother can affect birth weight. Gardosi et al (1992) did not concur with this, finding
instead that ethnicity affected birth weight but that stature did not.
Sabbagha et al
(1980) used serial ultrasound in the assessment of evolving macrosomia and suggested
that the abdominal circumference was the fetal parameter of choice for predicting
macrosomia.
Studies by Buchanan et al (1994) determined that ultrasound of the
abdominal circumference prior to 33 weeks gestation could identify Caucasian women at
risk of a macrosomic baby whilst studies by Hadlock et al (1984), Deter et al (1982) and
Benson and Doubilet (1998) all stressed the importance of the abdominal circumference
in fetal weight estimations. The fetal fat layer must be included in the measurement
(Picker 1982).
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5.2
ASUM vs Queen Mary Abdominal Circumference
The ultrasonic fetal measurement charts used in Australia are the Australasian Society for
Ultrasound in Medicine (ASUM) charts, which are based on a diverse ethnic population
mix. The Queen Mary Chart is commonly used in hospitals in Hong Kong and China,
and compared with the charts of both ASUM and Deter and Hadlock et al (Graphs 2/7 –
2/11), all fetal parameters are similar except for the abdominal circumference, which has
lower mean values in the last five weeks of gestation (Table 5/1).
Lai and Yeo
constructed fetal measurement charts based on the Asian population in Singapore which
also showed a difference in the abdominal circumference when compared with both the
ASUM and Deter charts and in 1981 Meire and Farrant suggested that ‘oriental’ babies
had a smaller mean abdominal circumference and a lower birth weight than white
European babies. If the abdominal circumference difference seen between ASUM AC
and the Queen Mary AC is reflected in our Chinese population then, when the AC is
included in a fetal weight formula, this relates to a smaller baby (Table 5/2).
Table 5/1 Abdominal Circumference Chart Comparison ASUM vs ‘Queen Mary’
_____________________________________________________________________
Weeks Gestation
33
34
35
36
37
38
39
40
41
ASUM mean
Abdominal Circumference (mm)
294
305
315
325
333
342
356
362
367
Queen Mary – mean
Abdominal Circumference (mm)
288
296
304
311
318
324
331
337
342
_____________________________________________________________________
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Applying the abdominal circumference figures from Table 5/1 to the following fetal
weight formula by Hadlock et al (1984), which incorporates the BPD, head
circumference, abdominal circumference and femur length, the weight differences are
demonstrated in Table 5/2.
Log10 (EFW in grams) = 1.3596 – (0.00386 AC FL) + (0.0064 HC) + (0.00061 BPD AC) +
(0.0424 AC) + (0.174 FL). Standard deviation (EFW) = +/- 7.5% of EFW (predicted mean).
Table 5/2
Weeks
Gestation
34 Weeks
36 Weeks
38 Weeks
40 Weeks
Caucasian/Chinese Weight Difference
Parameter
Mm
BPD 86
HC
305
FL
66
BPD 90
HC 317
FL
69
BPD 93
HC 328
FL
73
BPD 96
HC 340
FL
76
Caucasian
Weight
2388 +/- 358g
5lb 4oz
AC mm
Cauc
Chin
305
296
Chinese
Weight
2289 +/- 343g
5lb 1oz
2845 +/- 427g
6lb 4oz
325
311
2653 +/- 398g
5lb 14oz
3322 +/- 498g
7lb 5oz
342
324
3056 +/- 458g
6lb 12oz
3843 +/- 576g
8lb 8oz
362
337
3446 +/- 517g
7lb 10oz
As can be seen from Table 5/2, using the same BPD, HC and femur length but
substituting the AC for either ASUM or Queen Mary, there is a difference of almost 400
grams or 12 ounces at birth.
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5.3
Aims of Objective Four
1. To compare fetal size/growth in the third trimester of pregnancy in both Chinese
and Caucasian women with gestational diabetes mellitus and in Chinese
pregnancies with normal glucose levels.
2. To determine if any ultrasonically measured fetal parameter predicts an at risk
birth weight for Chinese or Caucasian babies and to determine if babies of
Chinese women with normal glucose levels have a lower mean birth weight than
either Caucasian or Chinese babies of mothers with GDM.
3.
To estimate the growth per day of fetuses with gestational diabetes mellitus in
both Caucasian and Chinese pregnancies.
5.4
Patient Selection Criteria
Criteria needed to be set to help determine which patients were to be included in the
study. Recruitment was via the antenatal clinics at both Hornsby Ku-Ring-Gai Hospital
and the Royal North Shore Hospital. Caucasian and Chinese women were the main focus
of the studies and it was necessary to further define Chinese as being born in China,
Taiwan or Hong Kong. At between 26 and 28 weeks gestation all patients coming
through these two clinics are screened for diabetes in pregnancy. This glucose challenge
test entails drinking 300ml of Glucaid containing a 50gram glucose load, within ten
minutes, then waiting for one hour, timed from the first sip, in which period the patient
cannot eat, drink or smoke. Blood is collected to measure the blood sugar level. Women
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with a glucose level equal to or greater than 7.8mm/litre are referred for a formal glucose
tolerance test (GTT). For three days prior to the GTT the patient has a high carbohydrate
diet with at least 150 grams of carbohydrate per day. After fasting overnight blood is
taken and if this fasting level is < 6mm/l the patient is given a drink containing a 75 gram
glucose load with further blood taken at 1 and 2 hours. Gestational diabetes is diagnosed
if any two of the three glucose readings are high. Normal levels are equal to or less than
5.2mm/l at 0 hours, 9.9mm/l at 1 hour and 8.5mm/l at 2 hours. Any Caucasian woman
testing positive to the formal GTT was invited to join the study provided the father of the
baby was also Caucasian. Chinese women both with and without gestational diabetes
were also required, for comparison, and so all Chinese women, with Chinese partners,
coming through the clinics were asked to participate. For those women who could not
speak or understand English it was necessary to obtain the services of either interpreters
or the midwives responsible for running the non-English speaking clinics. Hornsby
Hospital had its own Midwife interpreters who ran special clinics for non-English
speaking patients. These midwives play an integral role in helping the pregnant Chinese
women feel more relaxed with their confinement, and were also responsible for
explaining the research study, questionnaire and scanning procedure. At Royal North
Shore it was more difficult as antenatal clinic staff had to wait for the arrival of medical
interpreters before proceeding with appointments.
For this study, seventy-five women were eventually recruited from both clinics.
Twenty five Caucasian women with GDM, 25 Chinese women with GDM and 25
Chinese women without GDM, to be used as the control, were invited and accepted
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inclusion in the study after their glucose tolerance / challenge test at around 28 weeks
gestation.
The following criteria were to be met by each pregnant woman invited to participate:

Gestation of between twenty eight weeks and term

Known date of last menstrual period or a dating ultrasound in first trimester.

Singleton pregnancy with no fetal abnormalities seen on ultrasound examination

Glucose challenge /tolerance test at around 28 weeks gestation or earlier.

Caucasian woman with Caucasian partner, with gestational diabetes.

Chinese woman with Chinese partner, with or without gestational diabetes.
5.5
Subject Information Statement and Patient Consent
The patient information and consent form followed the format suggested by the Northern
Health Area Services Ethics Committee. The study explanation needed to be simple and
concise, remembering that some of the participants used English as a second language.
An abbreviated patient information was available in Chinese (Appendix 8A & 8B).
5.6
The Patient Questionnaire
This was the only study that required a patient questionnaire (Appendix 9).
The
information required related to the patients ethnicity, obstetric history and social history.
Two-thirds of the patients to be included in the study spoke English as a second language
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and so the questionnaire had to be available in both English and Chinese. With this in
mind, the questions needed to be clear, short and kept to a minimum. A Chinese medical
interpreter translated the questionnaire into Chinese and a Chinese midwife was present
to assist the patient in answering the questions in English. Each participant in the study
had their own individual folder to store a copy of the consent form, questionnaire, images
and measurement data. A separate copy of the consent form was placed into the medical
records of each participant.
5.7
Choosing the Ultrasonic Fetal Parameters
A longitudinal study was deemed to be most appropriate for the investigation of the effect
of gestational diabetes on fetal growth as fetal size was to be tracked from 28 weeks
gestation until term. The women recruited for the study were to be scanned at their
routine antenatal clinic visits and so no separate appointments were required. A fiveminute time span was estimated as being adequate to image and measure the required
fetal parameters. Only one sonographer, the author, was involved with data collection
and to avoid bias no reference was made to the previous ultrasound measurements.
It was necessary to decide which fetal measurement parameters were most
appropriate for determining fetal growth. Hadlock (1991) said that parameters should be
chosen based on their ease of measurement and the degree to which they can reflect
gestational age and growth. Measurements of the fetal head, abdomen and long bones are
needed to estimate gestational age/growth and, when applied to a formula, to give an
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estimation of fetal weight. Head measurements include the biparietal diameter (BPD),
head circumference (HC) and the occipito frontal diameter (OFD). The OFD is not as
common a measurement and is often ignored in preference to the HC. For this study it
was decided to incorporate both the OFD & HC as, particularly in late pregnancy, head
shape can distort the BPD measurement.
If the BPD is severely affected as in
dolichocephaly, it will only be used in a fetal weight formula if the cephalic index is
within the normal range. CI = (BPD/OFD) x 100% (Normal range = 73.9 - 82.7%). The
head circumference is less likely than the BPD to be affected by head shape due to
moulding and is therefore a reliable parameter to use in a weight formula.
The femur length has a linear relationship to the crown-heel length and is an
important parameter to add to any fetal weight formula as it makes allowances for
population differences. As well as the femur length, the humerus length was also chosen.
Researchers such as Benacerraf (1992) and Nyberg (1992) have linked shortened long
bones, in particular the humerus as one of the first parameters to alert to intra uterine
growth retardation.
Abdominal circumference (AC) measurements have been demonstrated to have a
linear relationship to the gestational age similar to the BPD and is the parameter that may
display fetal overgrowth by way of fat layer deposition (Picker 1982). It was necessary to
use this parameter, as the Queen Mary Hospital fetal measurement chart for the abdominal
circumference used in Hong Kong & Beijing is different to the abdominal circumference
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149
on the ASUM 2001 fetal measurement charts in the last few weeks of gestation. All other
fetal parameters are similar between the two sets of charts.
Fetal wellbeing was also to be examined and in the third trimester this involves
assessing the integrity of the placenta along with umbilical artery Doppler for analysis of
the flow velocity waveform. In the normal pregnancy there should be a progressive
increase in diastolic flow velocity with advancing gestation, which is believed to reflect
the progressive decreasing placental resistance. The most commonly used indices to
measure flow velocity are the systolic/diastolic ratio, resistive index and pulsatility index.
All three indices show similar predictive values when correlated against adverse perinatal
events and for this study the resistive index was chosen.
Normal waveforms are
unidirectional and demonstrate frequencies throughout the cardiac cycle.
Abnormal
waveforms reflect the placental resistance caused by damage to placental tertiary villi and
show decreased end-diastolic flow that may be absent or reversed. There are a number of
factors that affect the waveform including maternal position, fetal heart rate and fetal
compression of the cord. Other factors include technical errors such as the sampling site
too close to either the placenta or fetal abdominal insertion, the insonation angle and
Doppler gain.
5.8
Safety of Repeated Ultrasound Scans
The main purpose of this study was to record fetal growth in pregnant Chinese women,
both with & without gestational diabetes and Caucasian women with gestational diabetes.
The main concern with the Chinese women was the safety of repeated fetal ultrasounds
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on their unborn child and so they needed to be reassured that the scan would be brief. A
five-minute time span was estimated as being adequate to image and measure the
required fetal parameters. When first discussing this project with the Chinese midwives
from the Non-English Speaking Antenatal Clinic at Hornsby Hospital they mentioned the
fact that some Chinese women from traditional backgrounds are superstitious about any
tests during pregnancy.
Most of the women from this group had mothers and
grandmothers residing with them in Australia who strongly influenced any decisions
made in regard to diet, blood tests, type of labour and delivery. It was not surprising
therefore to be asked numerous questions on safety issues, not only by the mother-to-be
but also by her partner, mother or friend. The help of the Chinese midwives and medical
interpreters was invaluable in reassuring the women that the ultrasounds would take no
more than a few minutes and would not harm their baby. Only one non-diabetic Chinese
woman pulled out of the study, and was replaced by another candidate. The Caucasian
women had a totally different outlook towards the ultrasounds with only one being
slightly apprehensive and the others looking forward to seeing their baby each week.
5.9
Methodology
Fifty pregnant Chinese women were recruited from the Antenatal Clinics at either the
Royal North Shore Hospital or Hornsby & Ku-Ring-Gai Hospital. This represented
19.6% of total annual Chinese births for the two hospitals. Twenty-five Chinese women
had GDM (83% of total Chinese GDM pregnancies) and 25 Chinese women with a
normal glucose challenge test were included in the study (power 80%, df 2/40, d=0.65).
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Twenty-five Caucasian women with GDM were also recruited (56% of total Caucasian
GDM pregnancies). The percentage participation rate was based on the total from each
group and did not allow for further differentiation with partner ethnicity, which would
have increased the individual group percentages. As mentioned earlier, all Caucasian
women recruited had Caucasian partners and Chinese participants Chinese partners. This
was to ensure there was no bias due to a mix of ethnicity.
Maternal height, pre-
pregnancy weight and parity data was collected, with body mass index being within
normal range (15-29) for all participants. From 28 weeks gestation the women attended
the antenatal clinic at two to four week intervals till 36 weeks when weekly visits
commenced. All women with GDM were assessed at specialist antenatal clinics from the
time of diagnosis, where glucose levels and diet were closely monitored.
5.9.1 Fetal Parameters
At each antenatal visit from 28 weeks gestation a fetal ultrasound examination was
performed by the same sonographer, with the biometry measurements including the
biparietal diameter (BPD), head (HC) and abdominal circumference (AC), femur (FL)
and humerus lengths (HL) taken at the imaging planes recommended by ASUM (Chapter
Two). The relevant head image required for the measurement of the BPD, OFD and HC
is a transverse axial plane, which includes the falx cerebri anteriorly and posteriorly,
cavum septum pellucidum anteriorly in the midline, and the thalami.
The BPD is
measured at the widest point of the head from the outer edge of the nearest parietal bone
to the inner edge of the more distant parietal bone. The OFD is measured perpendicular
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to the BPD from mid to mid occipital bones. The head circumference can be traced
either with an ellipse mode or manually around the outer perimeter of the skull. The
imaging plane for the abdominal circumference is a true transverse cut at the level of the
fetal liver and stomach at the umbilical region. Although the AC can be measured using
the ellipse mode, in the third trimester it is usually more accurate to manually trace the
perimeter of the abdomen, including the fat layer. Long bones should be imaged in the
axial plane to achieve the longest length, with clean blunt ends and a strong acoustic
shadow behind the bone. Measuring must be along the diaphyseal shaft, excluding the
epiphysis.
The spectral Doppler analysis of the umbilical cord arteries is performed with the
patient in a semi recumbent position so as to minimise the risk of supine hypotension
syndrome due to compression of the inferior vena cava. Fetal movements/ hiccups
should be at a minimum before a free loop of cord is identified for sampling. The image
field is maximised, colour analysis activated, the pulsed wave Doppler cursor positioned
in one of the umbilical arteries and the Doppler gain set to a level where the spectrum can
be readily identified.
Three consecutive cardiac cycles are measured to reduce the
coefficient of variation of measurements to less than 5%.
5.9.2 The Data Collection Sheet Designs
Having set patient selection criteria and decided which parameters to measure, a data
collection sheet was designed with ease of use the main priority. For the gestational
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diabetes study a single sheet per patient was necessary with all information clearly set
out. Hospital identification stickers were used to reduce the risk of confusion and errors,
particularly with Chinese patients who used a western name as well as their traditional
Chinese names. Names were checked at every visit so as to avoid mistakes.
SCW PhD Research Project - HKH and RNSH Antenatal Clinics
NAME:
Gestational diabetes Y
N
Unit number:
LMP: 01/02/2002
G3
P2
DATE Gestation
BPD
OFD
HC
AC
FL
HL
AFI
EFW
RI
1/10
34w 2d
86
108
306
303
66
59
12
2440
6
15/10
36w 2d
90
112
317
325
69
62
15
2800
5.8
22/10
37w 2d
92
113
321
333
72
63
14
3280
5.7
5.9.3 Statistical Analysis
Statistical data used in this study was extracted from Northern Suburbs Area Health
Service OBSTET database. Statistical analysis was performed with SPSS for Windows
and Minitab with a one-way ANOVA and t-tests used to compare birth weights and
groups. As there is no statistically significant difference between any of the ASUM 2001
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and Deter/Hadlock fetal measurement charts in the final ten weeks of pregnancy (Chapter
2: Graphs 2/23 –2/27) only the ASUM charts were used for the final analysis. Scatter
graphs were created using Microsoft Excel with measurements superimposed onto the
ASUM fetal measurement graphs for each measured parameter, showing the mean
regression with plus and minus two standard deviations for each fetal parameter. A
Fisher Exact Probability was used to assess the individual hypothesis. Growth per day
for each fetus was calculated using the estimated fetal weight from 36 weeks of gestation
and between group comparisons utilized a two-way ANOVA.
5.10
Results
All women with GDM were assessed at specialist antenatal clinics from the time of
diagnosis, where glucose levels and diet were closely monitored and as a result none of
the study recruits required insulin therapy during the course of their pregnancy. No
significant difference was seen in the growth pattern between Chinese pregnancies with
normal GCT/GTT and those affected with gestational diabetes mellitus nor in the mean
birth weight of babies from the two groups.
There were 3,616 ultrasonic fetal measurements performed by the same
sonographer on 75 pregnant women during the third trimester. Twenty-five Caucasian
women with gestational diabetes mellitus (1144 measurements), 25 Chinese women with
GDM (1176 measurements) and 25 normal Chinese pregnancies (1296 measurements).
The mean number of ultrasound examinations for each woman was 6 (range 4–9).
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Unfortunately the assessment of the umbilical cord arteries by pulse wave
Doppler on all the pregnancies was incomplete due to technical difficulties encountered.
The RNSH ultrasound unit had a major system failure, which could not be repaired. The
initial system used at HKH was replaced by a unit, which did not have Doppler mode
available. Only twelve patients had completed umbilical cord Doppler analysis. All
resistive index readings taken were within the normal range.
Table 5/3
Birth Statistics
Northern Sydney
Health Statistics 2002
Total
Caucasian Births
Mean
Birth-weight
Gestational
Diabetics
GDM &
Macrosomia
Total births
Macrosomia
3435g
2.3%
11.1%
15.3%
+/- 502g
_______________________________________________________________________________
Total
Chinese Births
3344g
12%
6.7%
10%
+/- 464g
__________________________________________________________________
Study
Caucasians GDM
3485g
100%
20%
11.1%
+/- 449g
_______________________________________________________________________________
Study
Chinese GDM
3431g
100%
5%
5%
+/- 311g
_______________________________________________________________________________
Study
Chinese normal GTT
3352g
0%
0%
5%
+/- 244g
__________________________________________________________________
Table 5/3 compares the 2002 Northern Sydney Health Area mean birth weight, rate of
macrosomia and gestational diabetes for Caucasians and Chinese with this study. The
mean birth weights of the three groups in the study did not differ statistically from each
other nor from the Northern Sydney Health 2002 mean birth weights for Caucasian and
Chinese. Chinese (3352g) < Chinese GDM (3431g) < Caucasian (3435g) < Caucasian
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GDM (3485g). A two-way ANOVA with follow-up t-tests were done to compare birthweights between Northern Sydney Health statistics, Caucasian GDM, Chinese GDM and
Chinese control, which showed no statistically significant difference in birth weights,
suggesting that they probably came from populations with the same mean birth-weight.
The number of cases was insufficient for a logistic regression.
5.10.1 Chinese with and without GDM
No statistically significant difference in gestational age or birth weight was seen between
babies born to Chinese women with GDM (39wks 1day / 3431 grams) and those with
normal GCT (39wks 3days / 3352 grams). The average birth weight for all Chinese
babies in Northern Sydney Health Area was 3344g with the mean birth weight of males
being 42 grams heavier than for female babies. The influence of maternal age, body
mass index and parity on eventual birth weight was non-specific.
Of the 2472 fetal measurements taken from the Chinese population, 1176 were
affected by gestational diabetes and the remaining 1296 were normal Chinese
pregnancies. One woman with GDM gave birth preterm to a 3765g infant at 36 weeks 3
days and therefore was discarded from the study. Although there was only one GDM
birth over 4000g, another two babies could have had macrosomia, with one emergency
caesarean section at 38 weeks 3 days gestation weighing 3810g and another, the discard,
at 36 weeks 3days being 3765g. There was a 95% chance that the Chinese non-GDM
came from a population between 3230.3g and 3474g (actual 3352g) and Chinese GDM
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from a population between 3275.3g and 3585.7g (3431g). Eight GDM’s and nine nonGDM’s were above the mean Chinese weight with a total of nine of these babies
weighing over 3600 grams. Of these nine babies, eight (4 from each group) had an
abdominal circumference greater than the ASUM mean for at least three weeks from 34
weeks gestation (sensitivity 88.9%, specificity 97.6%). One baby with an AC > ASUM
AC mean at 35 and 37 weeks weighed 2958 grams. As 3600 grams is above the
estimated population mean for Chinese babies, the abdominal circumference was thought
to be a logical predictor for birth weight greater than 3600 grams in the Chinese
population. A Fisher exact probability of < 0.0000001 suggests that an AC greater than
the ASUM AC mean from 34 weeks predicts an at risk birth weight for our Chinese
population. A raised abdominal circumference prior to 34 weeks gestation gave a false
positive result as 22% of fetuses, seven GDM’s and two non-GDM’s, had an AC greater
than the ASUM AC mean before 34 weeks gestation which normalised after 34 weeks.
The head circumference was greater than one standard deviation above the ASUM HC
mean by 34 weeks gestation in seven GDM’s (birth weights 3390g, 3810g, 3595g, 3555g,
3380g, 4065g, 3750g) and three non-GDM’s (birth weights 3600g, 4290g, 3660g).
From 35 weeks gestation most fetuses of Chinese women, both with and
without GDM, had an abdominal circumference, which followed the mean of the Queen
Mary abdominal circumference graph (Graph 5/1).
The study results may indicate the
racial difference of fetal growth of the abdominal circumference with 3600 grams being
above the 90th percentile of the normal Chinese population in Australia. No statistically
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158
significant difference was seen for the BPD, HC, FL or HL (Graphs 5/2-5/6) between the
study groups and the general population based on the ASUM fetal measurement graphs.
5.10.2 Caucasians with GDM
There were 1144 ultrasonic fetal measurements performed on 25 pregnant Caucasian
women with gestational diabetes mellitus.
Each woman had between four and ten
ultrasound examinations performed, with a mean of seven scans, between 28 weeks
gestation and term. The mean birth weight of babies born to Caucasian women with
gestational diabetes mellitus was 3485 grams with a mean gestation of 39 weeks 4 days.
Birth weights were recorded for all 25 babies. Nine of these babies were above the mean
birth weight with four being macrosomic. Of those nine that were above the mean, six
had an abdominal circumference at least one standard deviation above the ASUM mean
by 35 weeks gestation.
Three of the four macrosomic fetuses had an abdominal
circumference two standard deviations above the ASUM mean at 30 weeks gestation but
by 35 weeks this had reduced to one standard deviation. There was a 95% chance that
the Caucasian GDM’s came from a population with a mean birth weight between 3260.2
grams and 3709.4 grams (actual mean weight 3485 grams). In 75% of the cases of
macrosomic births to Caucasian women with GDM both the head and abdominal
circumference were greater than one standard deviation above the ASUM HC & AC
mean by 35 weeks gestation.
Prior to 35 weeks there was no correlation between an
increased head and abdominal circumference and raised birth weight.
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5.10.3 Graph Comparisons – Caucasian/Chinese
The ultrasonic fetal measurements taken included the BPD, OFD, head and abdominal
circumference, femur and humerus lengths. No statistically significant difference was
seen for any of these parameters between the study groups and the general population
based on the ASUM fetal measurement graphs.
On the following set of graphs
measurements of the same value are superimposed.
Graph 5/1
Abdominal Circumference Comparison Scatter Graph
Abdominal Circumference (mm)
ASUM / Queen Mary / Caucasian & Chinese Gestational Diabetics
Chinese Non GD Abdominal Circumference
450
400
Ch NAC
C GD AC
Ch GD AC
350
Queen Mary
300
250
200
26
28
30
32
34
36
38
40
42
Weeks Gestation
Graph 5/1 is a scatter graph comparing the abdominal circumferences of normal Chinese
pregnancies (Ch NAC), Caucasians with GDM (C GD AC) and Chinese with GDM (Ch
GD AC). The figures have been superimposed onto the ASUM abdominal circumference
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160
graph showing the mean, plus/minus two standard deviations with the Queen Mary
abdominal circumference mean shown in red. The abdominal circumference of fetuses of
the 25 Caucasian women with gestational diabetes mellitus showed no significant
difference to the ASUM AC mean when the birth weight was appropriate for gestational
age. Fetuses of Chinese women, both with and without GDM with eventual mean
Chinese birth weight, had abdominal circumferences below the ASUM AC mean and
followed the mean of the Queen Mary abdominal circumference graph. Graph 5/2 shows
the individual group AC means - Queen Mary (red), Caucasian GDM (green), Chinese
GDM (blue) and normal Chinese (yellow). Note how the Caucasian mean is similar to
the ASUM mean whilst both the Chinese groups follow the mean of the Queen Mary
abdominal circumference.
Graph 5/2
Abdominal Circumference Comparison Line Graph
Abdominal Circumference
(mm)
Abdominal Circumference Comparison
ASUM (+/- 2SD), Queen Mary, Caucasian GDM, Chinese GDM
Chinese Non GM
420
400
380
360
340
320
300
280
260
240
220
200
180
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Weeks Gestation
160
161
Graph 5/3
Head Circumference Comparison Scatter Graph
Head Circumference (mm)
ASUM / Caucasian & Chinese Gestational Diabetics
Chinese Non GD Head Circumference
380
Ch NHC
Ch GD HC
C GD HC
360
340
320
300
280
260
240
220
200
26
28
30
32
34
36
38
40
42
Weeks Gestation
Graph 5/3 is a scatter graph of the group head circumferences superimposed onto the
ASUM head circumference curve with the mean and plus/minus two standard deviations.
There is no statistically significant difference seen between the normal Chinese
pregnancies (CH NHC), Chinese with GDM (CH GD HC) and the Caucasian pregnancies
with GDM (C GD HC). The outlier dots represent the macrosomic fetuses.
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162
Graph 5/4
BPD Comparison Scatter Graph
ASUM / Caucasian & Chinese Gestational Diabetics
/ Chinese Non GD BPD
120
110
BPD (mm)
Ch NBPD
100
Ch GDBPD
CGD BPD
90
80
70
60
26
28
30
32
34
36
38
40
42
Weeks Gestation
Graph 5/4 is the biparietal diameter scatter graph for the groups. There is no statistically
significant difference seen between the normal Chinese pregnancies (CH NBPD),
Chinese with GDM (CH GDBPD) and Caucasian GDM (CGD BPD).
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163
Graph 5/5
Femur Length Comparison Scatter Graph
Caucasian & Chinese Gestational Diabetics
Chinese Non GD / ASUM Femur Length
Femur Length (mm)
90
Ch NGD F
CGD FL
Ch GDFL
80
70
60
50
40
26
28
30
32
34
36
38
40
42
Weeks Gestation
Graph 5/5 is a scatter graph of the group femur lengths superimposed onto the ASUM
femur length curve with the mean and plus/minus two standard deviations. There is no
statistically significant difference seen between the normal Chinese pregnancies (Ch
NGD F), Chinese with GDM (Ch GDFL) and the Caucasian pregnancies with GDM
(CGD FL).
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Graph 5/6
Humerus Length Comparison Scatter Graph
Humerus Length (mm)
Caucasian & Chinese Gestational Diabetics,
Chinese non GDM / ASUM Humerus Length
80
75
70
65
Ch non GD
60
ChGD HL
55
CGD
50
45
40
26
28
30
32
34
36
38
40
42
Weeks Gestation
Graph 5/6 is a scatter graph of the group humerus lengths. There is no statistically
significant difference seen between the normal Chinese pregnancies (Ch non GD),
Chinese with GDM (ChGD HL) and the Caucasian pregnancies with GDM (CGD).
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5.10.4 Mean Measurements of Fetal Parameters
Mean fetal parameter measurements for each of the three groups from 32 weeks gestation
to term are shown in Tables 5/4 to 5/7.
The ASUM and Queen Mary mean
measurements are also shown.
Table 5/4
Weeks
Mean Abdominal Circumference Measurements.
28
29
30
31
32
33
34
35
36
37
38
39
40
242
259
262
272
283
294
305
315
325
333
342
356
362
241
264
278
282
283
288
302
322
324
333
340
343
361
247
258
261
269
278
297
304
313
314
316
324
327
332
245
248
260
266
272
287
295
306
308
315
324
332
333
244
253
262
271
280
288
296
304
311
318
324
331
337
Gestation
ASUM
AC mm
Caucasian
GDM AC
Chinese
GDM AC
Chinese
Non-GDM
Queen Mary
AC mm
Note how the abdominal circumference of the Chinese are similar to the Queen Mary AC
compared with the Caucasians and the ASUM figures. This was the only table to display
a variance between the Chinese and Caucasian groups.
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166
Table 5/5
Weeks
Mean Head Circumference Measurements
28
29
30
31
32
33
34
35
36
37
38
39
40
263
269
274
284
288
300
305
310
317
321
328
336
340
261
270
280
291
292
296
308
317
320
325
332
336
348
265
268
283
286
292
299
309
312
318
324
330
335
337
255
264
275
280
290
297
307
311
314
322
325
333
335
Gestation
ASUM
HC mm
Caucasian
GDM HC
Chinese
GDM HC
Chinese HC
Non-GDM
Table 5/6
Weeks
Mean Biparietal Diameter Measurements
28
29
30
31
32
33
34
35
36
37
38
39
40
72
75
76
80
81
84
86
88
90
92
93
95
96
70
75
78
79
79
81
83
88
89
90
91
93
95
72
74
76
78
82
84
85
86
88
90
91
93
95
72
73
78
79
81
83
84
86
88
90
91
93
94
73
75
78
80
83
85
87
89
91
92
94
95
96
Gestation
ASUM
BPD mm
Caucasian
GDM BPD
Chinese
GDM BPD
Chinese BPD
Non-GDM
Queen Mary
BPD mm
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167
Table 5/7
Weeks
Mean Femur Length Measurements
28
29
30
31
32
33
34
35
36
37
38
39
40
54
55
58
59
62
65
66
67
69
72
73
75
76
52
53
59
61
62
65
66
68
69
70
73
74
76
50
53
56
60
63
64
65
66
68
69
70
71
73
52
55
57
61
62
64
65
67
68
70
72
73
75
55
57
60
62
64
66
68
70
71
73
75
76
78
Gestation
ASUM
BPD mm
Caucasian
GDM BPD
Chinese
GDM BPD
Chinese BPD
Non-GDM
Queen Mary
BPD mm
5.10.5 Fetal Weight Gain in Pregnancies Affected by GDM
Fetal weight gain per day was calculated from 36 weeks of gestation (Table 5/8). A twoway ANOVA to compare group to average weight gain per day across the last four weeks
of gestation showed no statistically significant difference between the three groups
(F2,40=2.39, p=0.1) and no interaction between group and week (F6,120=0.38, p=0.89).
There was a significant linear trend across weeks with the weight gain in all groups
declining in the final four weeks of gestation (F1,40=13.78, p=0.001). Levene's test for
equality of variances was significant at 36 weeks. However, the results may be accepted
because the violation of equality of variances was not serious, it would tend to produce a
falsely significant group difference and interaction yet neither were noted here, and the
linear trend was supported by a Friedman rank order test at 36-37-38-39 weeks (2=8.45,
p=0.038).
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168
Table 5/8
Fetal Daily Weight Gain (grams/day)
Weeks
36
37
38
39
Caucasian GDM
29.6
28.6
27.5
27.2
Chinese GDM
27.3
26.9
26.8
25.6
Normal Chinese
25.2
24.7
23
21.8
5.11
Discussion
The careful monitoring of all women with GDM in our antenatal clinics resulted in none
of the studies 25 recruits requiring insulin therapy. It was initially hypothesised that the
GDM fetuses would have larger abdominal circumference and be heavier than the nonGDM fetuses, but with glucose levels so well controlled by diet and exercise this
hypothesis was rejected.
This study found that ultrasonic measurements of the fetal BPD, head
circumference and long bones were inconclusive for predicting large babies. This was in
agreement with Murata and Martin (1973) who measured the BPD of diabetic and nondiabetic pregnancies and found no significant difference. Whilst Buchanan et al (1994)
concluded that if ultrasound of the abdominal circumference was above the 75th
percentile as early as 29 weeks gestation it could be an identifier for macrosomia and
Benson and Doubilet (1995) indicated that an AC above the 90th percentile between 30
and 33 weeks of gestation has a predictive accuracy of 56% for macrosomia, this study
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169
concluded that in our Chinese population, ultrasound of the abdominal circumference
prior to 34 weeks gave a high level of false positives but that after 34 weeks an increased
abdominal circumference helped identify those fetuses that were larger than average and
therefore potentially at risk of birth complications.
The abdominal circumference difference seen between the ASUM and the Queen
Mary fetal measurement charts is reflected in our Chinese population and when these
differences are applied to a fetal weight formula (Hadlock et al 1984) incorporating the
BPD, HC, AC and FL the birth weight differences can be understood. Benson and
Doubilet (1998) found that in diabetic pregnancies the weight formula incorporating the
head, abdominal and femur measurements have a 95% confidence interval of 24%
compared with 15% in non-diabetic pregnancies due to the abdominal fat layer. The
smaller abdominal circumference and lower birth weight compared with the Caucasian
population seen in this study is also in agreement with the 1981 work of Meire and
Farrant and Woo and Wan (1984). For Chinese fetuses an abdominal circumference
greater than the ASUM abdominal circumference mean from 34 weeks gestation may
identify a birth weight above 3,600 grams, a size considered to be similar to macrosomia,
or birth weight over 4000 grams, in the Caucasian population, and so at risk for
intervention and post partum haemorrhage. In Chapter Four it was suggested that with
the high level of obstetric intervention (60%) and 20% incidence of post partum
haemorrhage amongst Chinese women with babies greater than 3500 grams, there may be
failure to detect pregnancies with fetal overgrowth.
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170
Chinese pregnancies thought to be small for gestational age were within the
normal range for Chinese and those pregnancies assessed as ‘normal’ were Chinese
women carrying bigger babies due to gestational diabetes mellitus or other genetic and
environmental factors. This is in agreement with the work of Homko et al (1995) who
thought that the interrelationship between gestational diabetes mellitus, ethnic variation
seen in fetal growth and fetal macrosomia was as a result of not only genetic factors but
influences of varying in-utero growth promoters in those populations.
With the
differences displayed in this study for the abdominal circumference and problems
associated with increased birth weight in the Chinese population the study agrees with
Spencer et al (1995) who thought it was inappropriate to use standard charts for
abdominal circumference and estimated fetal weight charts for Asian women due to their
lower body mass index. Although it is agreed with Sabbagha (1976), Parker (1981),
Hadlock et al (1990) and Arenson (1995) that racially specific growth charts are not
necessary, it is important to recognise, like Gardosi et al (1992), that ethnicity affects
birth weight.
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