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Hum. Reprod. Advance Access published online on February 21, 2008
Human Reproduction, doi:10.1093/humrep/den023
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© The Author 2008. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Embryonic staging using a 3D virtual reality system

C.M. Verwoerd-Dikkeboom1,3, A.H.J. Koning2, P.J. van der Spek2, N. Exalto1 and E.A.P. Steegers1

1 Department of Obstetrics and Gynaecology, Division of Obstetrics and Prenatal Medicine, PO Box 2040, Erasmus MC, University Medical Centre Rotterdam, 3000 CA Rotterdam, The Netherlands 2 Department of Bioinformatics, Erasmus MC, University Medical Centre Rotterdam, Rotterdam, The Netherlands

3 Correspondence address. Tel: +31-10-7032431; E-mail: c.verwoerd{at}erasmusmc.nl


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Supplementary material
 Acknowledgements
 References
 
BACKGROUND: The aim of this study was to demonstrate that Carnegie Stages could be assigned to embryos visualized with a 3D virtual reality system.

METHODS: We analysed 48 3D ultrasound scans of 19 IVF/ICSI pregnancies at 7–10 weeks’ gestation. These datasets were visualized as 3D ‘holograms’ in the BARCO I-Space virtual reality system. Embryos were staged according to external morphological features (i.e. mainly limb development). After staging, the crown rump length (CRL) was measured. Stage and CRL were compared with gestational age based on the date of oocyte retrieval and with the classical data on embryology from the Carnegie Collection.

RESULTS: Embryonic staging was relatively easy because the I-Space allows depth perception, which helps in the estimation of size and position. The presumed stages corresponded well with the measured CRL. However, in 28 out of 48 cases, the stages seemed to have been reached earlier than previously described for the Carnegie Collection.

CONCLUSIONS: The I-Space, tentatively named Virtual Embryoscopy, is a promising non-invasive tool for early pregnancy evaluation. Combining embryonic growth with embryonic development opens a new area to study the relationship between embryonic growth, development and morphology, as well as second and third trimester pregnancy complications.

Key words: Carnegie Stages/3D ultrasound/virtual reality/embryonic development


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Supplementary material
 Acknowledgements
 References
 
Adequate staging of embryonic development is important for an accurate description of normal development and provides insight in abnormal embryonic growth and development. Developmental embryonic staging was first employed in human embryology by Franklin Mall (1914), founder of the Department of Embryology of the Carnegie Institution in Washington. The Carnegie Staging system describes approximately the first nine weeks of pregnancy and the stages, numbered from 1 to 23, are based on internal and external physical characteristics of the embryo. At stage 23, all essential internal organ systems are present and this stage therefore represents the end of the embryonic period.

Blaas (1999)Go has already described that embryonic development visualized by ultrasound is in good agreement with the ‘developmental time schedule’ of human embryos, as described in the Carnegie Staging system. Although O’Rahilly and Müller (1987)Go stated that there are variations in embryonic age as well as in embryonic size, Blaas et al. (1998aGo, bGo) have shown that longitudinal ultrasound studies of normal embryos demonstrate virtually identical growth velocities for embryos and their associated structures. In their most recent study, 3D ultrasound was used to calculate volumes of human embryos and young fetuses (Blaas et al., 2006Go).

Wilhelm His (1880–1885Go) was the first who acknowledged the importance of 3D reconstructions of human embryos, making freehand drawings of histological slices. In the last decennia, development of computer technology has opened new possibilities for 3D reconstructions. The advantages of 3D ultrasound for fetal imaging in second and third trimester are unequivocal. The use of 3D ultrasound in the detection of fetal anomalies, especially for anomalies of face, limbs, thorax and spine is applied by numerous centres around the world (Timor-Tritsch and Platt, 2002Go). The use of 3D and 4D ultrasound in early pregnancy assessment was recently summarized by Zanforlin Filho et al. (2007)Go.

However, although these ultrasound datasets are three-dimensional, they are presented on flat 2D screens or paper, which implies that information concerning the third dimension, is not used optimally.

To benefit from all three dimensions we used a three-dimensional projection system, the I-Space. This virtual reality system immerses the viewer(s) in a three-dimensional virtual environment that allows the users to perceive depth and interact with the volume rendered data in an intuitive manner (Groenenberg et al., 2005Go).

Being able to accurately determine embryonic stages in the first trimester would provide a promising non-invasive tool for early pregnancy evaluation of embryonic growth and development. The aim of this study is to demonstrate that Carnegie Stages based on external morphological features can be assigned to embryos visualized with 3D ultrasound using this novel 3D virtual reality system. We tentatively name this technique as Virtual Embryoscopy.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Supplementary material
 Acknowledgements
 References
 
Patients
We analysed 3D ultrasound scans of 19 IVF/ICSI pregnancies. A total of 20 patients from the Department of Reproductive Medicine in our hospital volunteered, of whom 19 had ongoing pregnancies and one miscarried before six weeks gestational age. This patient was therefore excluded from our study. All patients were in good health, without any predisposing conditions or use of medication that could interfere with normal embryonic growth. Serial 3D ultrasound scans were made starting at ~26 days after oocyte retrieval until ~84 days after oocyte retrieval (corresponding with ~6 weeks gestational age until 14 weeks gestational age). This resulted in a total of 93 scans, varying from 3 to 9 scans per patient, with a median of 5 scans. A short analysis of the scans revealed that before Day 36 (corresponding with ~7 weeks gestational age), it was almost impossible to obtain images with high enough resolution to discern the fine details we needed for staging purposes. Since the Carnegie Staging System ends at stage 23, which corresponds with Day 57 according to O’Rahilly, we excluded all ultrasound scans made after the 57th day (corresponding with ~10 weeks gestational age). This resulted in a total of 48 ultrasound scans from 36 to 57 days after oocyte retrieval.

Ultrasound
Ultrasound scanning was performed on a GE Voluson 730 Expert system (GE, Zipf, Austria). The 3D volumes were transferred to a personal computer for off-line evaluation using specialized 3D software (4D view, GE Medical Systems). These data were then saved as cartesian (rectangular) volumes and transferred to the BARCO I-Space at the Department of Bioinformatics of the Erasmus MC. This is a 4-walled CAVE-like (Cruz-Neira, 1993Go) virtual reality system that uses passive stereo to immerse viewers in a virtual world. The images are generated by an SGI Prism visualization system with 8 graphics cards and are projected on three walls and the floor of a small ‘room’. The images need to be viewed through glasses with polarizing lenses in order to perceive depth. The CAVORE (Koning, 1999Go) volume rendering application is used to create a ‘hologram’ of the ultrasound volume that is being investigated, which can then be manipulated by means of a virtual pointer, controlled by a wireless joystick (Groenenberg et al., 2005Go). Wireless tracking of the viewer’s head allows the computer to provide a correct perspective and motion parallax which, in addition to the stereoscopic images, helps in discerning fine details and understanding of three-dimensional structures in the volumes.

The 48 volumes we obtained with 3D ultrasound were visualized in the I-Space as 3D ‘holograms’. Volumes were resized, turned and clipped to provide an unobstructed view of the embryo, and grey scale and opacity were adjusted for optimal image quality.

Staging
Embryos were staged according to the description of the external morphological features, mainly limb development, of the Carnegie Stages illustrated and described by O’Rahilly and Müller (1987)Go. After staging, the crown rump length (CRL) was measured. In the classical description, the CRL is better known as the greatest length of the embryo (Böhmer et al., 1993Go; O’Rahilly and Muller, 2000Go). Stage and CRL were compared with gestational age based on the date of oocyte retrieval and with the classical data on embryology described by O’Rahilly and Müller (Table I).


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  		Table I. Characteristics of Carnegie Stages 16 to 23 as described by O’Rahilly and Müller (1987)Go.

 
Statistical analysis was performed using SAS PROC MIXED, release 8.02 (SAS Institute Inc, Cary, NC, USA). For analysis of the longitudinal measurements, we used repeated measurements ANOVA (random coefficient model).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Supplementary material
 Acknowledgements
 References
 
In all 48 ultrasound scans, we were able to determine the Carnegie Stage of the embryo easily (Figs 1–3 and Supplementary Data, Movie S1). Curvature of the elbow for instance, which distinguishes stage 19 from stage 20, was quite obvious, as was the position of the limb buds or hands and feet. In 12 out of 48 cases, we believed the Carnegie Stage to be in between two stages, for instance, at stage 17–18.


Figure 1
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  		Figure 1: I-Space picture of an embryo, age 39 days after oocyte retrieval.

The presumed stage is stage 17

 

Figure 3
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  		Figure 3: Embryo of age 56 days after oocyte retrieval.

The presumed Carnegie Stage is stage 23

 
The measured greatest lengths (Table II) show a high degree of uniformity with the length reported for that stage by O’Rahilly. Figure 4 shows the comparisons of the individual length measurements in the I-Space with the lengths for the corresponding stage that O’Rahilly reported. From this figure, it is clear that for stage 23 the measured lengths are in all cases substantially larger than reported. Two CRL measurements (stages 17–18 and 19, respectively), representing one patient (number 19 in Table II), are clearly above the 95th percentile. After birth, no abnormalities were found and birth weight was at the 50th percentile. Therefore, these findings remain unexplained.


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  		Table II. Individual measurements and staging details of all examinations in 9 patients.

 

Figure 4
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  		Figure 4: Comparisons of the lengths of the individual measurements of our study group in the I-Space (grey dots) with the range of lengths O’Rahilly reported for the different stages (in black)

 
We also found that in our study, the age determined by the date of oocyte retrieval was younger than that which O’Rahilly reported for the corresponding Carnegie Stage. This is demonstrated in Fig. 5, which shows the comparison of embryonic age according to the date of oocyte retrieval with the embryonic age reported by O’Rahilly for that stage. Of 48 ultrasound scans, only 18 cases had a Carnegie Stage with an age that corresponded with O’Rahilly’s report. In two cases, the age was one day older than according to the Carnegie Stage. In 28 cases, the age was younger than the lowest value for that stage given by O’Rahilly, varying from 1 to 5 days younger. The individual patterns of growth per embryo are displayed in Fig. 6. ANOVA showed an average daily increase in length of 1.08 mm (0.04 SEM).


Figure 5
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  		Figure 5: Comparison of the days after oocyte retrieval of our study group (grey dots) with the age range reported by O’Rahilly for the different stages (in black)

 

Figure 6
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  		Figure 6: Individual growth patterns per embryo

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Supplementary material
 Acknowledgements
 References
 
With this study, we successfully demonstrate that embryonic growth and development can be classified into Carnegie Stages using innovative imaging techniques. Until now, growth and development during the embryonic period is commonly only defined by its age and/or length exclusively. The embryonic period is generally believed to demonstrate uniform growth (Blaas, 1999Go) and therefore biometry measurements are generally based on the comparison of measured values with predicted values derived from reference charts or equations from normal populations. However, differences in growth and development in normal embryos have been described in several studies (Dickey and Gasser, 1993Go; Smith et al., 1998Go; Deter et al., 1999Go; Bukowski et al., 2007Go). Recently, Bukowski et al. (2007)Go described the relationship between fetal growth in early pregnancy and the risk of delivering a low birth weight infant. Numerous articles have been published about measuring and estimating human embryonic and fetal age (Kellokumpu-Lehtinen, 1984Go; Todros et al., 1991Go; Böhmer et al., 1993Go; Blaas, 1999Go; O’Rahilly and Muller, 2000Go; Degani, 2001Go; Salomon et al., 2003Go; Salomon et al., 2005Go; Sladkevicius et al., 2005Go). Apart from in pregnancies from assisted fertility programmes, the exact gestational age is difficult to establish. IVF/ICSI pregnancies however create new dilemmas such as the question of whether embryonic growth in these pregnancies is similar to growth in normally conceived pregnancies (Dickey and Gasser, 1993Go; Wisser et al., 1994Go; Wennerholm et al., 1998Go; Tunon et al., 2000Go; Sladkevicius et al., 2005Go).

For many species, growth and development is classified into stages based on the morphological state of development. The Carnegie Staging System has proven its value in the classification of human embryos for decennia. It does, however, have some limitations. For instance it is important to remember that embryologists generally use embryos obtained following spontaneous miscarriage (where the embryos may have died in utero a few days before the miscarriage) and that these embryos are fixated. Hence it is not known how well they represent normal development (Harkness et al., 1997Go). In 1977, Drumm and O’RahillyGo assessed prenatal age from the CRL determined ultrasonically in vivo and in utero in cases with ‘known post-ovulatory age’. In this study, the CRL determined ultrasonically agreed well with those in length/age tables in embryologic literature. However, for a given age the ultrasonic lengths were 1 to 5 mm longer than those in fixed specimens. With this knowledge, Drumm and O’Rahilly adjusted the ages of the embryos in the Carnegie Collection to the ultrasonic findings.

Using 2D ultrasound it is very difficult to exactly determine morphologic features during the embryonic period and thus only a few articles have been published about the use of the Carnegie Staging System in the evaluation of embryos using ultrasonography (Böhmer et al., 1993Go; Blaas et al., 1998aGo, bGo; Smith et al., 1998Go). Three-dimensional ultrasound offers a better view of these features; it does however require a skilled sonographer with up to date knowledge of the 3D ultrasound software to optimize the use of the entire data set. We present a new imaging technique, using volume renderings in virtual reality. It offers an easy to interpret 3D image with depth perception and one can interact with volume rendered (ultrasound) data in an intuitive manner.

This study compares ‘in vivo’ observations of human embryos, with well-established fertilization dates, using high-resolution ultrasound imaging, with data on miscarried and fixated embryos with known post-menstrual ages. The embryos in our study seemed to reach a Carnegie Stage at an earlier gestational age than O’Rahilly described. In our study the assignment of a Carnegie Stage is purely based on external morphological features and completely neglects the inner features. Still, we are confident that the assignment is accurate. A morphological study using terminated pregnancies by Harkness and Baird (1997)Go showed, that although they used more than one parameter for definite classification, identification of stages 14 to 23 primarily based on limb development is feasible. Therefore we are reluctant to explain the age difference this way. A possible explanation may be that the original ages of the Carnegie Collection and the ages after the adjustments made by Drumm and O’Rahilly are all based on menstrual history and basal body temperature, which are not completely reliable. Since we used pregnancies of assisted fertility programmes, this could also explain the age discrepancy.

We conclude that the I-Space offers an impressive new way of looking at growth and development during embryogenesis. We emphasize that measuring size alone does not adequately reflect embryonic growth and development. The Carnegie Staging system is a well-established method that enables focusing on morphological features. Hence, combining length measurements with viewing developmental features using virtual reality techniques, will greatly improve knowledge of normal and abnormal embryonic growth, development and morphology. Virtual Embryoscopy opens the way for studying the relationship between embryonic growth, development and morphology as well as second and third trimester pregnancy complications.


   Supplementary material
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Supplementary material
Acknowledgements
 References
 
Supplementary material is available at HUMREP Journal online.


Figure 2
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  		Figure 2: Picture of an embryo in the I-Space, age 53 days after oocyte retrieval.

The presumed Carnegie Stage is 22–23 (same embryo as embryo in Supplementary Data, Movie S1)

 


   Acknowledgements
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Supplementary material
 Acknowledgements
References
 
We would like to thank Dr Joop Laven for his constructive comments on the manuscript and the staff of the Department of Reproductive Medicine at the Erasmus MC for their help in recruiting the patients. We would also like to thank Wim Hop of the Department of Biostatistics at the Erasmus MC for his help with the statistical analysis.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Supplementary material
 Acknowledgements
 References
 
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Submitted on October 24, 2007; resubmitted on December 12, 2007; accepted on December 20, 2007.


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