The ESHRE Special Interest Group in Embryology published the Atlas of Embryology in 2000 as a supplement to Human Reproduction. This initiative was received with acclaim and has become a very valuable reference that is used by embryologists all over the world.
We have undertaken to produce a new edition that completely updates the first edition and have chosen to publish it as an online document that provides the additional advantages of flexibility for revision and ease of consultation. The ease of online publication means that the Atlas can be updated on a regular basis and we intend, in the first update, to add chapters on cryopreservation and time-lapse monitoring. The new edition includes almost 400 figures grouped in four chapters: the oocyte, the zygote, the cleavage stage embryo and the blastocyst. Each chapter has a brief introduction and is then divided into several subheadings which are described by a short text and by a series of images whose features are detailed in a legend and, when needed, by specific diagrams. Our aims were to share knowledge among embryologists and to contribute a visual illustration of a common language for scoring and grading human oocytes and preimplantation embryos. As a reference, we have used the document produced by the Istanbul consensus workshop published as a joint venture between Alpha Scientists and the ESHRE Special Interest Group in Embryology. We believe it is essential to adopt a common language for scoring and grading human embryos and hope that the illustrations within this Atlas will assist in this process and encourage all embryologists to use this language when describing embryos in the medical literature.
Despite the many changes that have occurred in the field of IVF since publication of the first edition of the Atlas, the observation of oocyte and embryo morphology remains a very valuable tool in clinical embryology. One of the most important parameters introduced by the Istanbul consensus meeting is the need for standardization of the times of assessment during the successive days of culture from oocyte retrieval. The blastomere number and size in relation to the time of development, the presence of fragments in the perivitelline space and the appearance of the cytoplasm are the most important non-invasive parameters that guide embryo selection for transfer or cryopreservation. We have also undertaken to illustrate several morphological features of preimplantation development, the consequences of which, to implantation potential, remain unclear. It is hoped that the next revision of this Atlas will include the new information provided by continuous monitoring of embryo development and how the morphological features relate to implantation potential. Although our experience as embryologists suggests that the kinetics of embryo development along with an accurate morphological assessment is a good predictor of viability, it is clear that the process of implantation includes several factors that may not be directly related to the embryo. Therefore, even though we have made reference to the outcome of transfer whenever available in the Atlas, this information must be interpreted in the general context of the many factors that can influence the outcome of embryo transfer.
The editors wish to thank Luc Vanoppen for his assistance in all phases related to image submission and processing; the members of the Human Reproduction team who have worked on the production of the Atlas, especially Joanne Mason whose expert input significantly improved this volume; Caroline Bracken from Oxford University Press for assisting us in all steps related to the publication of the Atlas and finally ESHRE for having supported us in realizing this project.
We would also like to thank all those who contributed photographic material and particularly the chapters' editors who organized the corresponding texts and figures.
Very special thanks to Gayle Jones who acted as a Project Co-ordinator for the Atlas. Her unconditional dedication and expertise made the completion of the Atlas possible.
We hope that The Atlas of Human Embryology: From Oocytes to Preimplantation Embryos will become a valuable tool for every embryologist, not only in their clinical work but also for learning and teaching purposes.