In a growth phase occurring during most of folliculogenesis, the oocyte produces and accumulates molecules and organelles that are fundamental for the development of the preimplantation embryo. At ovulation, growth is followed by a phase of maturation that, although confined within a short temporal window, encompasses modifications of the oocyte chromosome complement and rearrangements of cytoplasmic components that are crucial for the achievement of developmental competence. Cumulus cells (CCs) are central to the process of maturation, providing the oocyte with metabolic support and regulatory cues. PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews concerning oocyte maturation in mammals. Searches were performed adopting ‘oocyte’ and ‘maturation’ as main terms, in association with other keywords expressing concepts relevant to the subject. The most relevant publications, i.e. those concerning major phenomena occurring during oocyte maturation in established experimental models and the human species, were assessed and discussed critically to offer a comprehensive description of the process of oocyte maturation. By applying the above described search criteria, 6165 publications were identified, of which 543 were review articles. The number of publications increased steadily from 1974 (n = 7) to 2013 (n = 293). In 2014, from January to the time of submission of this manuscript, 140 original manuscripts and reviews were published. The studies selected for this review extend previous knowledge and shed new and astounding knowledge on oocyte maturation. It has long been known that resumption of meiosis and progression to the metaphase II stage is intrinsic to oocyte maturation, but novel findings have revealed that specific chromatin configurations are indicative of a propensity of the oocyte to resume the meiotic process and acquire developmental competence. Recently, genetic integrity has also been characterized as a factor with important implications for oocyte maturation and quality. Changes occurring in the cytoplasmic compartment are equally fundamental. Microtubules, actin filaments and chromatin not only interact to finalize chromosome segregation, but also crucially co-operate to establish cell asymmetry. This allows polar body extrusion to be accomplished with minimal loss of cytoplasm. The cytoskeleton also orchestrates the rearrangement of organelles in preparation for fertilization. For example, during maturation the distribution of the endoplasmic reticulum undergoes major modifications guided by microtubules and microfilaments to make the oocyte more competent in the generation of intracellular Ca²⁺ oscillations that are pivotal for triggering egg activation. Cumulus cells are inherent to the process of oocyte maturation, emitting regulatory signals via direct cell-to-cell contacts and paracrine factors. In addition to nurturing the oocyte with key metabolites, CCs regulate meiotic resumption and modulate the function of the oocyte cytoskeleton. Although the importance of oocyte maturation for the achievement of female meiosis has long been recognized, until recently much less was known of the significance of this process in relation to other fundamental developmental events. Studies on chromatin dynamics and integrity have extended our understanding of female meiosis. Concomitantly, cytoskeletal and organelle changes and the ancillary role of CCs have been better appreciated. This is expected to inspire novel concepts and advances in assisted reproduction technologies, such as the development of novel in vitro maturation systems and the identification of biomarkers of oocyte quality.

BACKGROUND: The relationship between early embryo post-implantation development in couples undergoing assisted reproductive techniques (ARTs) and sperm chromatin alterations has not been satisfactorily explained. The aim of this study was to assess the relationship between sperm DNA fragmentation in IVF/ICSI patients, sperm parameters (concentration, motility and morphology) and ART outcome, especially with regard to clinical pregnancy and pregnancy loss (spontaneous miscarriage or biochemical pregnancy). METHODS: DNA fragmentation was evaluated by TUNEL assay, performed on sperm suspensions after density gradient separation, in 132 men undergoing an ART cycle (82 IVF and 50 ICSI) and correlated with sperm parameters and ART outcome. RESULTS: A highly significant negative correlation was found between DNA fragmentation and sperm parameters. There was a close relationship between DNA fragmentation and post-implantation development in ICSI patients: the clinical pregnancy and pregnancy loss rates significantly differed between patients with high and low sperm DNA fragmentation (P = 0.007 and P = 0.009, respectively). CONCLUSIONS: Sperm DNA fragmentation seems to affect embryo post-implantation development in ICSI procedures: high sperm DNA fragmentation can compromise ‘embryo viability’, resulting in pregnancy loss.

STUDY QUESTION Which recommendations can be provided by the European Society of Human Reproduction and Embryology Special Interest Group (ESHRE SIG) Embryology to support laboratory specialists in the organization and management of IVF laboratories and the optimization of IVF patient care? SUMMARY ANSWER Structured in 13 sections, the guideline development group formulated recommendations for good practice in the organization and management of IVF laboratories, and for good practice of the specific procedures performed within the IVF laboratory. WHAT IS KNOWN ALREADY NA. STUDY DESIGN, SIZE, DURATION The guideline was produced by a group of 10 embryologists representing different European countries, settings and levels of expertise. The group evaluated the document of 2008, and based on this assessment, each group member rewrote one or more sections. Two 2-day meetings were organized during which each of the recommendations was discussed and rewritten until consensus within the guideline group was reached. After finalizing the draft, the members of the ESHRE SIG embryology were invited to review the guideline. PARTICIPANTS/MATERIALS, SETTING, METHODS NA. MAIN RESULTS AND THE ROLE OF CHANCE The guideline provides recommendations on the general organization of an IVF laboratory (staffing and direction, quality management, laboratory safety), and on the specific aspects of the procedures performed in IVF laboratories (Identification of patients and traceability of their reproductive cells, consumables, handling of biological material, oocyte retrieval, sperm preparation, insemination of oocytes, scoring for fertilization, embryo culture and transfer, and cryopreservation). A last section provides recommendations regarding an Emergency plan for IVF laboratories. LIMITATIONS, REASONS FOR CAUTION Evidence on most of the issues described is scarce, and therefore it was decided not to perform a formal search for and assessment of scientific evidence. However, recommendations published in the EUTCD and relevant and recent documents, manuals and consensus papers were taken into account when formulating the recommendations. WIDER IMPLICATIONS OF THE FINDINGS Despite the limitations, the guideline group is confident that this document will be helpful to directors and managers involved in the management and organization of IVF laboratories, but also to embryologists and laboratory technicians performing daily tasks. STUDY FUNDING/COMPETING INTEREST(S) The guideline was developed and funded by ESHRE, covering expenses associated with the guideline meetings. The guideline group members did not receive payment. Dr Coticchio reports speaker's fees from IBSA and Cook, outside the submitted work; Dr Lundin reports grants from Vitrolife, personal fees from Merck Serono, non-financial support from Unisense, outside the submitted work; Dr. Rienzi reports personal fees from Merck Serono, personal fees from MSD, grants from GFI, outside the submitted work; the other authors had nothing to disclose. TRIAL REGISTRATION NUMBER NA.

STUDY QUESTION: What recommendations can be provided on the approach to and use of time-lapse technology (TLT) in an IVF laboratory?SUMMARY ANSWER: The present ESHRE document provides 11 recommendations on how to introduce TLT in the IVF laboratory.WHAT IS KNOWN ALREADY: Studies have been published on the use of TLT in clinical embryology. However, a systematic assessment of how to approach and introduce this technology is currently missing.STUDY DESIGN, SIZE, DURATION: A working group of members of the Steering Committee of the ESHRE Special Interest Group in Embryology and selected ESHRE members was formed in order to write recommendations on the practical aspects of TLT for the IVF laboratory.PARTICIPANTS/MATERIALS, SETTING, METHODS: The working group included 11 members of different nationalities with internationally recognized experience in clinical embryology and basic science embryology, in addition to TLT. This document is developed according to the manual for development of ESHRE recommendations for good practice. Where possible, the statements are supported by studies retrieved from a PUBMED literature search on ‘time-lapse’ and ART.MAIN RESULTS AND THE ROLE OF CHANCE: A clear clinical benefit of the use of TLT, i.e. an increase in IVF success rates, remains to be proven. Meanwhile, TLT systems are being introduced in IVF laboratories. The working group listed 11 recommendations on what to do before introducing TLT in the lab. These statements include an assessment of the pros and cons of acquiring a TLT system, selection of relevant morphokinetic parameters, selection of an appropriate TLT system with technical and customer support, development of an internal checklist and education of staff. All these aspects are explained further here, based on the current literature and expert opinion.LIMITATIONS, REASONS FOR CAUTION: Owing to the limited evidence available, recommendations are mostly based on clinical and technical expertise. The paper provides technical advice, but leaves any decision on whether or not to use TLT to the individual centres.WIDER IMPLICATIONS OF THE FINDINGS: This document is expected to have a significant impact on future developments of clinical embryology, considering the increasing role and impact of TLT.STUDY FUNDING/COMPETING INTEREST(S): The meetings of the working group were funded by ESHRE. S.A. declares participation in the Nordic Embryology Academic Team with meetings sponsored by Gedeon Richter. T.E. declares to have organized workshops for Esco and receiving consulting fees from Ferring and Gynemed and speakers’ fees from Esco and honorarium from Merck and MSD. T.F. received consulting fees from Vitrolife and Laboratoires Genévrier, speakers’ fees from Merck Serono, Gedeon Richter, MSD and Ferring and research grants from Gedeon Richter and MSD. M.M. received sponsorship from Merck. M.M.E. received speakers’ fees from Merck, Ferring and MSD. R.S. received a research grant from ESHRE. G.C. received speakers’ fees from IBSA and Excemed. The other authors declare that they have no conflict of interest.TRIAL REGISTRATION NUMBER: N/A.DISCLAIMER: This Good Practice Recommendations (GPR) document represents the views of ESHRE, which are the result of consensus between the relevant ESHRE stakeholders and are based on the scientific evidence available at the time of preparation.ESHRE’s GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care nor exclusive of other methods of care reasonably directed to obtaining the same results. They do not replace the need for application of clinical judgment to each individual presentation, nor variations based on locality and facility type.Furthermore, ESHRE GPRs do not constitute or imply the endorsement, or favouring of any of the included technologies by ESHRE.†ESHRE Pages content is not externally peer reviewed. The manuscript has been approved by the Executive Committee of ESHRE.

BACKGROUND: Recently, interest in oocyte cryopreservation has steadily increased. Newly developed protocols have dramatically improved survival rates, removing perhaps the major hurdle that has prevented this approach from becoming a fully established form of treatment. However, the clinical efficiency of these protocols has not been exhaustively explored and therefore remains controversial. METHODS: Morphologically normal oocytes displaying the first polar body were frozen–thawed with a slow cooling protocol that utilized 1.5 mol/l propane-1,2-diol (PrOH) and 0.3 mol/l sucrose. RESULTS: A total of 927 oocytes from 146 patients were frozen–thawed, achieving a 74.1% survival rate. Over 76% of microinjected oocytes displayed two pronuclei 16 h post-insemination, while the proportion of embryos at 44–46 h post-insemination was 90.2%. At this time point, the majority (68.3%) of embryos were at the two-cell stage, showing in most cases (78.7%) minimal or moderate fragmentation. Eighteen clinical pregnancies, three of which were twin, were observed, giving rise to rates of 12.3 and 9.7%, calculated per patient and per embryo transfer, respectively.The implantation rate was 5.2%. To date, four children have been born and three pregnancies resulted in spontaneous abortions, while the remaining pregnancies are ongoing. CONCLUSIONS: Our data indicate that although the combination of slow cooling and high sucrose concentration ensures high rates of oocyte survival, it is not sufficient to guarantee a high standard of clinical efficiency.