Middle East Fertility Society Journal (2013) 18, 115–119

Middle East Fertility Society

Middle East Fertility Society Journal

www.mefsjournal.orgwww.sciencedirect.com

ORIGINAL ARTICLE

Three-dimensional ultrasonography using the VOCAL

technique for estimation of reference range between

7 and 11 weeks embryonic volumeq

Hassan Mostafa Gaafar, Ghada Abdel Fattah Abdel Moety, Waleed El-Khayat *

Department of Obstetrics and Gynecology, Faculty of Medicine, Cairo University, Cairo, Egypt

Received 26 November 2012; accepted 25 December 2012Available online 4 February 2013

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KEYWORDS

VOCAL;

Embryonic volume;

Three-dimensional

ultrasonography

N.B. the study has been appro

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ourad Street, Giza 12211, Egmail addresses: waleedelkhay

yahoo.com (W. El-Khayat).

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Abstract Objective: Accurate estimation of gestational age (GA) is the basis of vital decisions in

pregnancy and hence its importance in obstetric management. This study tries estimating a refer-

ence range of 3D embryonic volume using the VOCAL technique for pregnancies between 7 and

11 weeks.

Materials and methods: This cross-sectional study included 62 singleton normal uneventful preg-

nancies. All women were essentially sure of the date of last menstrual period. All women were sub-

mitted to 3D ultrasonographic examination with VOCAL technique to determine the embryonic

volume. In addition the crown-rump length was measured. Regression analysis was performed to

predict the gestational age from the fetal volume.

Results: There was a strong positive correlation between embryonic volume and menstrual age,

gestational age and crown-rump length (r = 0.919, 0.938 and 0.941, respectively). Power regression

model produced R2 value of 0.838 with a regression equation (y= 52.22 + 6.5 x).

Conclusion: This study demonstrated that embryonic/fetal volume is a good predictor of gesta-

tional age with a power regression equation (y= 52.22 + 6.5 x) for the period from 7 to

10 weeks + 6 days. We suggest using the embryo volume as an early evidence of growth restriction

in high risk pregnancy.� 2013 Middle East Fertility Society. Production and hosting by Elsevier B.V. All rights reserved.

e Institutional Review Board.

ura Ibn Shourik Street, Off

bile: +20 100 513 55 42.alainy.edu.eg, waleed_elkhyat

dle East Fertility Society.

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1. Introduction

Accurate estimation of gestational age (GA) is the basis of vi-tal decisions in pregnancy and hence its importance in obstetricmanagement. The first trimester is considered optimal for ges-tational age estimation with ultrasonography as the individual

biologic variations are insignificant (1) and the increments ofultrasound parameters are constant (2). Crown-rump length(CRL) has been proved to be a reliable parameter for the esti-

mation of pregnancy age especially from 6 to 9 weeks (3).

y Elsevier B.V. All rights reserved.

Figure 1 3D multiplanar view of an embryo 10 weeks.

116 H.M. Gaafar et al.

CRL is known to be dependent on the fetal position at thetime of scan and may be affected by minor changes in fetal po-

sition (4). To overcome this, some authors recommended threeCRL measurements to calculate their average recorded whichmay be a time-consuming process (5,6). Another issue is that

CRL considers only a single dimension of the fetus. The fetusis essentially a three-dimensional object, thus having a volumethat should be considered to estimate fetal growth.

Three-dimensional ultrasound is the best way for measure-ment of irregularly shaped objects through tracing of the outersurface of irregularly shaped objects rather that estimating vol-ume through mathematical formulas (7).

Embryonic volume was previously assessed using differentsoftware systems. Blaas et al. (8) employed the EchoPAC-3Dsystem that allows geometric reconstruction of different body

parts through multiple parallel bidimensional planes. Aviramet al. (9) used the virtual organ computer-aided analysis (VO-CAL) method with a 30-degree rotation angle. Falcon et al.

(10) and Martins et al. (11) measured fetal trunk and head vol-ume by three-dimensional ultrasound in normal pregnanciesand those conceived by in vitro fertilization. Araujo-Junioret al. (12) employed the more recently developed XI VOCAL

volumetric technique.The aim of this study was to estimate a reference range of

3D embryonic volume using the VOCAL technique for preg-

nancies between 7 and 11 weeks (Fig. 1).

2. Materials and methods

This is a cross-sectional study that included 62 singleton preg-nancies with a live embryo at 7–11 weeks’ gestation betweenJanuary 2012 and September 2012 in Kasr El-Aini Maternity

Hospital. All participants provided a written informed con-sent. We included women with normal uneventful pregnancies

who are sure of their menstrual dates with history of regularcycles. Women with chronic diseases and history of recurrent

abortions were excluded.

2.1. Ultrasonographic examination

All sonographic exams were performed at the Fetal MedicineDepartment, Kasr Al Aini, Cairo University using an E6equipment (GE, USA) with an endocavitary volumetric 4–

9 MHz probe. Two examiners performed all ultrasound mea-surements. A stepwise measurement using the VOCAL tech-nique was performed as follows: the dataset containing theembryo was initially displayed on the screen in three orthogo-

nal planes (Figs. 2 and 3). The sagittal view of the embryo wasdisplayed in plane A (top left image) and this image was ro-tated so that the orientation of embryo was coincident with

the Y-axis. Two demarcating arrows were positioned at eachend of the embryo to define its limits to be included in the vol-ume calculation. Plane A (coincident with the longitudinal

view of the embryo) was selected in the multiplanar display,and volume estimates were computed utilizing the VOCALprogram with a manual tracer at 30� rotation. The outer aspectof the embryo was drawn on every image displayed sequen-tially in this plane. At the end of the 180� rotation, the builtin software calculated the volume automatically. Before thiscalculation was accepted, the image in Plane A was scrolled

up and down repeatedly so that contouring imperfectionscould be corrected in the corresponding axial section exposedin plane C (bottom left image). This software tool allows the

performance of volume measurements by rotating the organor structure of interest around a fixed axis, while 2D contoursare manually or automatically delineated on each plane.

Different rotation angles (6�, 9�, 15� and 30�) for each con-tour plane can be selected, which are indirectly related to the

Figure 3 CRV by VOCAL corresponding to 9 weeks + 4 days.

Figure 2 VOCAL of a CRV corresponding to 9 weeks.

Three-dimensional ultrasonography using the VOCAL 117

number of rotation steps necessary to perform the measure-

ments. For this study, we used a rotation angle of 30� sinceit allows the quickest possible measurements with no signifi-

cant compromise in accuracy when compared to lower rota-

tion angles (13). The external contours of six sequentialplanes were manually outlined. At the end of the process,

Table 1 Descriptive values of the embryonic volume for each week.

Gestational age (week) N Mean Median Standard deviation Minimum Maximum CI 95%

7–7 + 6 12 0.42 0.41 0.2333 0.35 0.5 0.35–0.5

8–8 + 6 17 1.15 1.401 0.615 0.37 1.85 0.369–1.85

9–9 + 6 14 1.806 1.48 0.926 0.69 3 0.687–3.01

10–10 + 6 21 3.108 3 0.539 2.5 4 2.5–4

6.0

7.0

8.0

9.0

10.0

11.0

6.0 7.0 8.0 9.0 10.0 11.0

GA from CRL

GA

from

feta

l vol

ume

r = 0.950p < 0.001

Figure 4 Correlation of fetal volume and CRL.

118 H.M. Gaafar et al.

the equipment automatically added all the outlined areas and

displayed the final embryonic volume.To calculate inter- and intra observer reproducibility, one

observer performed fetal volume measurement of 30 embryostwice and the other examiner measured the same cases once

without prior knowledge of measurements of the firstexaminer.

2.2. Statistical analysis

Data were collected on a 2007 Excel spreadsheet (Microsoft,Redmond, WA) and analyzed using SPSS for Windows, ver-

sion 17.0 (SPSS Inc., Chicago, IL). Mean, median, standarddeviation (SD) and maximum and minimum values were ob-tained. The 95% confidence interval for each week was calcu-

lated. Correlation between embryonic volume and crown-rump length and gestational age was determined using thePearson method followed by regression analysis. Regressionanalysis was performed to predict the gestational age from

the embryonic volume. The intraclass correlation coefficient(ICC), Bland–Altman graphs, and paired Student’s t (p) testwere used to compare data. Significance was established at

p< 0.05.

3. Results

Sixty-four normal pregnancies, 7–10 + 6 weeks, were in-volved. The mean menstrual age was 9.1 ± 1.2 weeks, whilegestational age determined by ultrasonography was

9.0 ± 1.2 weeks. The mean difference between the two read-ings was 0.09 ± 0.22 weeks, which was statistically significant(p = 0.032). The mean CRL was 23.7 ± 9.0 mm (range 9–

38 mm). Mean embryonic volume was 1.7 ± 1.2 cm3 (range0.35–4.0 cm3). Table 1 shows descriptive values of the embry-onic volume for each week.

There was a strong positive correlation between embryonicvolume and menstrual age, gestational age and crown-rumplength (Fig. 4) (r= 0.919, 0.938 and 0.941, respectively).Regression analysis was performed to predict the gestational

age from the embryonic volume. Power regression model pro-duced R2 value of 0.838 with a regression equation(y = 52.22 + 6.5 x) where y= gestational age, x = embry-

onic volume. Using this equation the predicted gestationalage fitted well with that predicted from CRL with a minimaldifference and a p value of 0.234.

There was a good inter- and intra-observer reproducibilityfor embryonic volume. The inter-observer correlation coeffi-cient = 0.997 (95% confidence interval [CI]:0.992–1.00), andthe intra-observer correlation coefficient = 0.994 (95% CI:

0.988–0.998).

4. Discussion

This study demonstrated a strong correlation between fetalvolume estimation and crown-rump length measurement forthe prediction of gestational age (r= 0.950). Embryonic/fetal

volume is a good predictor of gestational age with a powerregression equation (y = 52.22 + 6.5 x) for the period from7 to 10 weeks + 6 days.

Embryo volume measurement using 3D ultrasonographywas tried by several authors with different methods of estima-tion. In the current study we used the VOCAL technique

which was previously used with a reasonable accuracy(9,14,15). Lee et al. (16) employed this technique for determi-nation of gestational sac volume in early pregnancy with clin-ically acceptable bias and agreement with the 2D ellipsoid

model measurement. Similar to our results, Aviram et al. (9)reported a significant correlation between embryonic volumeand crown rump length. Rolo et al. (14) suggested an exponen-

tial equation model to the correlation between embryo volumeand gestational age. However, Sur et al. (15) found that sonog-raphy-based automated volume count (SonoAVC) was more

reliable than the manual technique for embryo volumemeasurement.

In the current study, the embryo volume ranged from a

mean of 0.42 ± 0.233 (0.35–0.50 cm3) at 7 weeks to3.11 ± 0.539 (2.50–4.00 cm3) at 10 weeks + 6. A similar trialin Brazil to estimate a reference range for embryo volume re-ported different results with a wider range from

0.20 ± 0.23 cm3 to 5.12 ± 1.57 cm3 (12). These authors mea-sured embryonic volume using the XI VOCAL technique withmanual outline of 10 sequential planes. This might explain the

difference. Nevertheless, the two methods were found to be

Three-dimensional ultrasonography using the VOCAL 119

concordant in the assessment of gestational sac volume be-tween 7 and 11 weeks (17).

In fact, embryo volume seems to be a better reflection of fe-

tal growth rather than the CRL. This is because the embryovolume increases 7.8 folds while the CRL increases 2.9 foldsover the 4-week period from 7 to 11 weeks. Thus, we suggest

using the embryo volume as an early evidence of growthrestriction in high risk pregnancy. Its use for gestational agedetermination is nearly accurate as CRL which is simpler

and depends on 2D rather than the more expensive and sophis-ticated 3D ultrasonography.

Conflict of interest

All authors have nothing to disclose.

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