الفهرس 
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Abstract
Summary
EFBW is needed especially when head measurement is
impossible, because the fetal head is positioned low in the
pelvic brim. A convenient method for estimating fetal body
weight without head measurement was thus required.
Isobe (2004) derived a formula from only thigh measurements using conventional two dimensional
ultrasound. The derived formula was quite simple, involving only two thigh parameters without the need for
head measurement.
The aim of this study was to evaluate the accuracy of using only 2 thigh parameters ; Femur Length ( F L ) and
Cross Sectional Area of the Thigh ( CSAT ) , together with the newly established Isobe’s formula for estimation of fetal body weight at third trimester, in comparison with the
well established Hadlock formula.
This prospective study was performed at Ain Shams University Maternity Hospital between August 2012 and
February 2013. It included 105 pregnant ladies in their third
trimester, who delivered by elective cesarean section in than 72 hours after having two dimensional ultrasound
examinations.
All cases participated in the study were subjected to:
Verbal consent.
Detailed history reviewing.
Detailed clinical examination.
Ultrasound examination.
Elective cesarean section.
All measurements were performed by an expert sonographer in the fetal ultrasound unit using a transabdominal
ultrasound with 5.0 MHz convex probe
(Medison SonoAce X6). Parameters like Bi-parietal
diameter (BPD), Abdominal Circumference (AC), Femur
length (FL) and Cross sectional area of thigh (CSAT) were
measured respectively.
The estimated fetal body weight was calculated twice as follow:
1- Using Hadlock’s formula, which had been calculated
by the machine programmed software, using BPD, AC
and FL.
2- Using Isobe’s formula, which had been calculated
manually using FL and CSAT as follow:
EFBW = 13 × (FL × √CSAT) + 39 (gm).
N.B: FL by millimeter, CSAT by centimeter.
The birth weight (BW) of the infant was measured
immediately after delivery. This prospective study was
analyzed and evaluated by comparing the results of
EFBW using the previously illustrated newly established
Isobe’s formula [using femur length (FL) and cross
sectional area of the thigh (CSAT)] and already
established commonly used Hadlock formula [using biparietal
diameter (BPD), abdominal circumference (AC) and femur length (FL)] with actual birth weight.
Actual birth weight was taken as the gold standard.
Differences among estimated weights from the Isobe
formula, Hadlock formula and the actual birth weight was
assessed by a paired t test and corrected chi-squared test.
The mean actual birth weight in included women was
3217.8 ± 573.03 g. Of the 105 included neonates, 88
(83.8%) had average birth weight [2500 – 4000 g], 10
(9.5%) had low birth weight [<2500 g], while 7 (6.7%) had
large birth weight [> 4000 g].
There was a significant positive correlation between
actual birth weight and each of EFW using Hadlock’s
formula, EFW using Isobe’s formula. The highest
correlation coefficient was with EFW using Isobe’s
formula [r=0.924, p˂0.01], indicating the most significant
association.
The mean paired difference between EFW using Hadlock’s formula and actual birth weight was -100.07 ±
326.24 g [95% CI (-163.21 to -36.94 g); p=0.002]. The
mean paired difference between EFW using Isobe’s
formula and actual birth weight was 62.16 ± 230.37 g [95%
CI (17.57 to 106.74 g); p=0.007]. The narrower 95% CI
and the high p value for the Isobe’s formula when compared to Hadlock’s formula denote closer values of the
estimated fetal weight to the actual birth weight using the
former formula than the latter one.Of note, the mean paired
difference was positive in Isobe formula (i.e. the error
toward overestimation) while Hadlock formula has a
negative mean for the paired difference (i.e. the error is
toward underestimation).
Among the average birth weight category, the mean
paired difference was lower when Isobe’s formula rather
than Hadlock’s formula was used [-36.46 ± 188.98 g vs.
90.15 ± 322.48g]. The difference was positive in Hadlock’s
formulae [denoting an overestimating error] while negative
in Isobe’s formula [denoting an underestimation error].
Among the low birth weight category, Isobe formula
had mean paired difference markedly higher than that
noticed among the average birth weight category, and it
was noted that the Hadlock’s formula had negative mean
paired difference while it was positive in average birth
weight. In addition Hadlock’s formula had lower mean
paired difference & tight range when compared to the
Isobe’s formula [-85.4 ± 209.3g vs. -455.7 ± 200.26 g]. The
mean was negative in both formulae [denoting an
underestimating error].
Among the large birth weight category, Hadlock’s
formula had mean paired differences markedly higher than
that noticed among the average birth weight category, and
it was noted that Isobe’s formula had positive and higher
mean paired difference when compared to that of average
birth weight. both Hadlock’s formula and had positive
mean paired difference [489.7 ± 187.86 g vs. 177 ± 85.9 g].
The difference was positive in both formulas [denoting an
overestimating error