Abstract and Introduction
Abstract
During the past decade, cryopreservation of oocytes and embryos has become one of the most exciting areas in human-assisted reproduction. Improvement of the old techniques and introduction of alternative procedures have radically increased the overall efficiency and extended applicability. In parallel, the development of other laboratory techniques (embryo culture and preimplantation diagnostics) as well as medical, social, legal and cultural demands required the rapid and widespread exploitation of the new possibilities. This review summarizes the main features of the technical development, including both achievements and controversies, and outlines the emerging assisted reproductive technique strategies based partially or predominantly on cryopreservation. Application of these new achievements may substantially modify our approach in many fields and increase the overall efficiency of infertility or fertility preservation treatments.
Introduction
Cryopreservation of oocytes and embryos is a fashionable subject of reviews. This is not only the subjective impression of the authors, it can be justified by a simple PubMed search for 'cryopreservation' or 'vitrification' or 'freezing', and 'oocyte' or 'embryo', with the additional filters for '10 years', 'humans' and 'review', resulting in 360 hits, with 87 of them focusing primarily on cryopreservation (based on individual evaluation of abstracts performed by authors). The corresponding numbers of randomized controlled trials during this period were only 69 and 27, respectively. Accordingly, the publication of another review does not improve the 'too much talk, too few work' situation, and can only be justified by sound reasons.
One of our arguments is that out of the 486 thematic papers published in the seven volumes of Expert Review of Obstetrics and Gynecology, only three (including a short Editorial) is dealing with embryo and oocyte cryopreservation. The number is disproportionally low, especially if it is compared with the 14 articles dealing with the undoubtedly interesting but much less practiced preimplantation genetic diagnosis/screening.
Additionally, our review is also addressed to infertility doctors and embryologists who are marginally or actively involved in cryopreservation. According to our experience, this sparkling subject is still full of controversies, and repeated arguments supported with newly published sound evidences may convince those who have some doubts regarding the way ahead. Moreover, we will also deal with some new, exciting developments, that – if confirmed by future studies – may further improve the efficiency of cryopreservation and the whole assisted reproduction.
The main purpose of our work is to provide a general picture about the state of the art; the de facto and potential benefits of the recently introduced cryopreservation techniques; what are the current limitations and setbacks; and how can we accelerate the advancement towards a standardized, widely accepted, simple and reliable new cryopreservation approach that may profoundly change the current practices in human-assisted reproductive techniques (ART).