Journal of Islamabad Medical & Dental College (JIMDC); 2015:4(4):147-151
Original Article
Accuracy of Ultrasound Examination at Term
Pregnancy in Estimation of Fetal Weight
Mohammad Wasim Awan1, Farhat Jehan2, Nadia Rashid3, Saima Ather4, Aneela Abid5
HOD Radiology Department, KRL General Hospital, Islamabad
2,4,5PG Trainee Radiology, KRL General Hospital, Islamabad
3Senior Medical Officer Radiologist, KRL General Hospital, Islamabad
1
estimating low birth weight was 88.63%.
Conclusion: In our study, the mean estimated
weights through ultrasound were similar to mean
actual weight. Hence, despite of controversies in
literature, our results indicate the diagnostic accuracy
of ultrasound in estimation of low birth weight to be
considerably significant.
Keywords: Fetal weight, Diagnostic accuracy
Ultrasonography.
Abstract
Objective: To determine the diagnostic accuracy of
ultrasound estimation of fetal weight in low birth
weight fetuses in term pregnancies keeping actual
birth weight as gold standard.
Materials and Methods: This cross sectional
study conducted in department of Radiology, KRL
hospital, Islamabad from 29-02-2012 to 31-08-2012.
Two
fiftyfive
cases
using
non-probability
Convenience sampling were taken. Pregnant patients
at term presenting in the radiology department of
KRL Hospital for ultrasound examination were
included in the study. Informed written consent was
taken from the patient. Ultrasound examination and
fetal weight estimation through measurements all
parameters of fetus was carried out by consultant
radiologist using GE Logic P/6 three Dimensional
machine. An addition of 25 g per day was done to
correct the time elapsed between the ultrasound and
delivery. After birth the weight of new born was
recorded within 2 hours of birth.
Results: A total of 255 patients who presented in
radiology department for antenatal ultrasound at
term pregnancy were recruited for study. The mean
age of all patients was 29.73±4.065 SD (Range 20-38
years). The estimated fetal birth weight (g) through
ultrasound was shown as low in 169 (62.27%)
whereas actual birth weight was low in 184 (72.16%).
Thus, the sensitivity, specificity, positive predictive
value and negative predictive value of ultrasound to
determine
low
birth
weight
fetuses
was
80.04%,90.14%, 95.88% and74.45% respectively. The
diagnostic accuracy of ultrasound in correctly
Introduction
Both low birth weight and excessive fetal weight at
delivery are associated with an increased risk of
newborn and maternal complications during labor and
the puerperium.1,2 The perinatal complications
associated with low birth weight are most often
attributable to fetal prematurity. For macrosomic
fetuses potential complications associated with
delivery include shoulder dystocia, brachial plexus
injuries, bony injuries, and intrapartum asphyxia, as
well as maternal risks that include birth canal injuries,
pelvic floor injuries damage, and postpartum
hemorrhage.3
The correct determination of fetal weight prior to
delivery accurately is of utmost important and greatly
influences the clinical management, the outcome of
pregnancy, delivery and survival of newborn
especially in cases of fetal growth restriction. Fetal
weight estimation is a good predictor of fetal growth
and this may affect the timing and route of delivery.4
In low birth weight babies, the option for suppression
of labor can be given to the women while Option for
labor induction can be considered in women carrying
oversized fetuses. Various methods are used to
estimate fetal weight at birth.5,6 These include
Predicting fetal weight through clinical examination,
using algorithms derived from parental and pregnancyspecific characteristics, maternal self-estimation and
Address for Correspondence:
Dr. Muhammad Wasim Awan
E-mail: [email protected]
Received: Sept 9th 2015; Accepted: Jan 16th 2016
147
Journal of Islamabad Medical & Dental College (JIMDC); 2015:4(4):147-151
through
ultrasound
examination.7,8
Obstetric
sonographic assessment for the purpose of obtaining
fetal biometric measurements to predict fetal weight
has been presumed to be more accurate than clinical
methods for estimating fetal weight through fetal
biometric measurements. One study showed that
sensitivity, specificity, positive predictive value and
negative predictive value for ultrasonic detection of
low fetal weight in non-diabetic women were 61%,
96%, 69% and 94% respectively.9
The incidence of low birth weight is around 37%.10
Although sonographic assessment of fetal weight is
more accurate than the clinical examination, there is a
quite variation in the reported diagnostic accuracy in
previous studies. The aim of this study was to
determine the diagnostic accuracy of ultrasound
estimation of fetal weight in low birth weight fetuses
in term pregnancies keeping actual birth weight as
gold standard.
were recruited for study. The mean age of all patients
was 29.73±4.065 with minimum of 20 and maximum
of 38 years. Out of total 255 patients, 96 (37.65%)
were primipara parity and 159 (62.35%) showed
multiparity. Average ultrasound estimated fetal weight
(g) was 2449.31±257.454 (g) with minimum of 1965g
and maximum of 3021g. The variability in observed
data in form of range was observed as 1065g. Mean
actual birth weight was calculated to be
2406.08±279.926g with minimum actual weight
observed as 1900g and maximum actual weight
observed as 3200g. (Table 1)
Table I: Descriptive Statistics of Patient Age (years),
Fetal weight by USG (grams) and Actual birth weight (g)
Age
Fetal weight by
USG
Actual birth
weight
29.73
2449.31
2406.08
Std. Deviation 4.065
Mean
Material and Methods
Pregnant patients at term, both primigravida and
multigravida presenting in the radiology department of
KRL Hospital for ultrasound examination were
included in the study. Stillbirths, multiple pregnancies,
patients with elapse time of >3 weeks between
ultrasound estimation and delivery and patients with
diabetes mellitus and hypertension were excluded
from the study. Informed written consent was taken
from the patient. The data was collected on the
Performa attached. Ultrasound examination and fetal
weight estimation through measurements all
parameters of was carried out by consultant radiologist
using GE Logic P/6 three Dimensional machine. The
Fetal weight in grams was recorded on the Performa.
An addition of 25 g per day was done to correct the
time elapsed between the ultrasound and delivery.
After birth the weight of new born was recorded
within 2 hours of birth.
The Statistical Package for social sciences Version 13
(SPSS 13) was used for data analysis. Continuous
variables such as age were expressed in as mean ±
Standard Deviation. Frequency and percentage was
calculated for qualitative variable true positives. The
accuracy of EFW through ultrasound was calculated
using formula for accuracy (True positive, True
negative, False positive, False negative)
257.454
279.926
Minimum
20
1956
1900
Maximum
38
3021
3200
The estimated fetal birth weight (g) through
Ultrasound was shown as low in 169 (62.27%)
whereas actual birth weight was low in 184 (72.16%).
Thus, the sensitivity of ultrasound (ability to correctly
identify fetus having low birth weight) was 80.04%
whereas specificity of ultrasound (ability to correctly
identify fetus not having low birth weight) was
90.14%. The positive predictive value (probability of
having low birth weight babies on ultrasound when it
is actually present) was observed as 95.88% and
negative predictive value (probability of having low
birth weight babies on ultrasound when it is actually
not present) was 74.45%. The diagnostic accuracy of
ultrasound in correctly estimating low birth weight
was 88.63%. (Table 2)
Table 2: Cross-tabulation of Low fetal weight (US)
vs Actual low birth weight
Actual low birth
weight
Total
Yes
No
Low fetal weight (US)
Results
Total
A total of 255 patients who presented in radiology
department for antenatal ultrasound at term pregnancy
148
Yes
162
7
169
No
22
64
86
184
71
255
Journal of Islamabad Medical & Dental College (JIMDC); 2015:4(4):147-151
integrates FL and AC only that is not affected via such
alterations.16
The Basic underlying assumption for Sonographic
measurements is that the multiple linear as well as
planar dimensions of fetus give enough parametric
information for allowing the precise algorithmic
reconstruction of 3 dimensional fetal volumes for
varying tissue density.17 Hence we conducted this
study to assess the diagnostic accuracy of ultrasound
estimation of fetal weight in low birth weight fetuses
in term pregnancies keeping actual birth weight as
gold standard.
Total 255 patients who presented in radiology
department for antenatal ultrasound at term pregnancy
were recruited in our study. The mean age of all
patients was 29.73±4.065 with minimum of 20 and
maximum of 38 years. Other factors as lack of
education, poverty and poor socio-economic status
also contribute in early pregnancies and associated
complications.18
Among total 255 patients, 37.65% patient were
primipara and 62.35% showed multipara parity. In one
study in United States Population, it was found that
primipara-multipara curves had significant impact on
low birth weight of infants.19 Average ultrasound
estimated fetal weight (g) was 2449.31±257.454 (g)
with variability in observed data was observed as
1065g. Mean actual birth weight was calculated within
2hours after birth to be 2406.08±279.926g. The
difference in estimated and actual birth weights was
not much different in our study.
In our study, further, the estimated fetal birth
weight(g) through Ultrasound was shown as low in
169 (62.27%) whereas actual birth weight was low in
184 (72.16%). Thus, the sensitivity of ultrasound
(ability to correctly identify fetus having low birth
weight) was 80.04% whereas specificity of ultrasound
(ability to correctly identify fetus not having low birth
weight) was 90.14%. The diagnostic accuracy of
ultrasound in correctly estimating low birth weight
was 88.63%. The above mentioned study focusing on
the diagnostic accuracy of ultrasound in determination
of fetal weight showed that the sensitivity, specificity,
positive predictive value, and negative predictive value
for ultrasonic detection of fetal weight ≥4000 g among
the non-diabetic women were 61%, 96%, 69%, and
94%, respectively whereas in detection of fetal weight
≥4500, the figures were 50%, 98%, 47%, and 98%,
respectively.20
Discussion
Low birth weight is the most crucial element that not
only causes neonatal mortality but also plays a
significant role in post neonatal infant mortality as
well as of infant morbidity.11 WHO, in 1979, presented
the most comprehensive results of LBW that was
updated later in 1982. Out of total 127 million babies
who were born in 1982, about 20 million that
constitutes 16% had been estimated for having LBW.
Astonishing fact in this study was that the lowest birth
weights were found to be in Asia having average
values from approx. 2700 - 2800g in Indian subcontinent to 3200-3300g in China and Japan and
analogous Low Birth Weight rate of 30 – 40 % and 5 –
6 % respectively. Whilst in the West Africa the
average birth weight was found to be 2800 - 3000 g
with rate of Low Birth Weight to be 10 – 20 % whilst
in the North Africa mean range of weight was 32003300 g and LBW was 5 – 15 %.12
Particularly, significant focus has been posed on the
causes for determining birth weight, specially
determining low birth weight of infants. So that, any
intervention could be made for modifying these risk
factors.13 Ultrasound is a technique basically used to
estimate fetal weight in order to ascertain the growth,
timing and route of delivery as well as to detect any
abnormality as fetal growth abnormality or genital
problems.14 For estimation of low birth weight
ultrasound is considered to be more precise, whilst for
normal clinical examination and above 4000g range,
both clinical examination and ultrasound give
somewhat similar level of accuracy.15
One prospective study concluded that the Hadlock2
method predicts birth weight more precisely compared
to others. Also, the average deviation from actual birth
weight (226gms) and the percentile value of absolute
error for difference were minimum with above
mentioned method, and it predicts maximum numbers
of the cases in 10 % of the actual birth weights (85%).
A significant difference had been observed between
predicted and the actual birth weight in rest of the
methods (p<0.01). Hence the conclusion was that
Hedlock2 method is comparatively better predictor for
birth weights compared to the other six and also, it is
method of choice for estimation of the birth weights in
term pregnancy where measurements of the foetal
head were frequently seen to be imprecise that may
either be due to engagement or molding because it
149
Journal of Islamabad Medical & Dental College (JIMDC); 2015:4(4):147-151
3.
Additionally, another study focused on determining
the accuracy of ultrasound in estimation of the fetal
weight among 246 parous women having singleton,
term pregnancies who had been admitted for caesarean
section. In this study, sensitivity and specificity of
estimating birth weight through ultrasound measures
was 12.6 % and 92.1 %. Also, the estimates by
clinicians for birth weight in the term pregnancy were
as much precise as the routine ultrasound in a week
before the delivery. Also, the estimates for parous
women for birth weight were even more precise
compared to ultrasound estimation.21
One study demonstrated the sensitivity, specificity,
positive predictive value and negative predictive value
for ultrasonic detection of low fetal weight in nondiabetic women were 61%, 96%, 69% and 94%
respectively.9 On one side are studies similar to that by
Colman A et al showing sensitivity and specificity as
50% and 98% for ultrasound estimation of fetal weight
while on the other side are studies similar to that by
Ashrafganjooei T et al showing sensitivity and
specificity as 82% and 62%.21
It is therefore evident through our results which are
similar to many other studies that ultrasound
technique, despite of the ongoing debates and
controversies, plays a significant role in estimation of
low birth weight and still is a reliable source for
diagnosis of fetal weight.
4.
5.
6.
7.
8.
9.
10.
Conclusion
11.
In our study, the mean estimated weights through
ultrasound were similar to mean actual weight. Hence,
despite of controversies in literature, our results
indicate
the
diagnostic
accuracy
of ultrasound in estimation of low birth weight to be
considerably significant.
12.
13.
Conflict of Interest
14.
This study has no conflict of interest as declared by
any author.
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