Now, a (nearly) 3-year collaboration of 17 internationally recognised experts from the same organisations has produced a comprehensive update. After systematically reviewing the literature and deliberating on current evidence, they have developed a new set of recommendations. The updated Istanbul Consensus is published simultaneously in Human Reproduction and Reproductive Biomedicine Online and is freely accessible to all readers (2, 3).
The new consensus outlines 20 key recommendations, refining morphological assessments from the oocyte to the blastocyst stage. Particular emphasis has been placed on optimising the timing of embryo evaluations, integrating insights from time-lapse microscopy. Additionally, duration of culture, prioritisation criteria for embryo selection, and the emerging role of artificial intelligence (AI) have been discussed. To provide context for these updates, a global survey was conducted, to collect data on current laboratory practices and the implementation of the Istanbul Consensus (2011). The survey results are tabulated and presented alongside the recommendations. Therefore, the updated consensus represents a significant advancement in both methodology and clinical applicability.
The document is organised based on developmental chronology, beginning with oocytes. Many features of the oocyte have been identified as being correlated to fertilisation and development potential. Yet, an exhaustive review revealed that evidence only supports exclusion of so-called giant oocytes from clinical use. It is acknowledged, however, that prenatal follow-up and the follow-up of babies born from oocytes with atypical phenotypes and rescue IVM demands attention. While zygotes with two pronuclei (2PN) remain preferred, the consensus recommendation is to cautiously consider 1PN and 2.1PN configurations in combination with preimplantation genetic testing for aneuploidy (PGT-A), specifically to confirm biparental diploidy.
One major change in the updated recommendations is the refinement of the timing for key developmental assessments. Fertilisation checks are now recommended at 16 to17 hours post-insemination (hpi) for both ICSI and conventional IVF, based on time-lapse evidence. Nuance has been introduced to cleavage stage checks with early cleavage assessments recommended at 26 hpi for ICSI and 28 hpi for IVF. Median times to reach the 4-cell and 8-cell stages are identified as 38 and 57 hpi for ICSI embryos but one hour later for IVF embryos. These changes may be unexpected or unfamiliar to many practitioners without time lapse experience, but following these guidelines should improve the reliability of embryo evaluations and better align morphological assessments with underlying biological events.
At the cleavage stage, embryos exhibiting less than 10% fragmentation, mononucleation, and stage-specific cell size are prioritised. However, the consensus also recommends that cleavage-stage embryos with such atypical features should be placed in extended culture to determine their development potential, recognising the embryo’s inherent plasticity.
Blastocyst evaluation is based on the Gardner grading system, with focus on expansion stage, and inner cell mass (ICM) and trophectoderm (TE) morphology. Evidence now suggests that Day-7 blastocysts and those graded with lower morphological scores (grade C for ICM and/or TE) are potentially viable and may be suitable for clinical use. Thus, a further grade โDโ is added to the Gardner scheme to classify blastocysts with degenerative features or absence of a distinct ICM, to distinguish them from those with poor (grade C) quality. To guide ranking of blastocysts for transfer, an elaborate table is introduced for both fresh and frozen embryos.
Despite advances in the understanding of human gametes and embryos in vitro, the consensus deliberations revealed that many knowledge gaps persist. Morphological and morphokinetic abnormalities identified at fertilisation, for instance, continue to pose interpretative challenges and provide opportunities for future research, particularly using time-lapse technologies.
The consensus also addresses the emerging role of artificial intelligence (AI) in embryo selection. The potential of these technologies to provide objective, quantitative assessments of gametes and embryos is exceedingly clear. Further development of AI-driven analytic tools may allow more accurate identification of the most viable embryo(s) and improve embryo selection strategies.
Finally, it is important to emphasise the critical role of international collaboration in advancing clinical embryology. By bringing together diverse expertise and experiences, the consistency of research methodologies can be increased and clinical outcomes can be improved. The ultimate goal remains unchanged: to improve the quality of care for patients undergoing assisted reproduction and to increase the likelihood of successful outcomes. This updated consensus marks a pivotal step towards that goal.
References
1 Alpha Scientists in Reproductive Medicine and ESHRE Special Interest Group Embryology. Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting. Hum Reprod. 2011 Jun;26(6):1270-83. doi: 10.1093/humrep/der037. (and simultaneously in Reprod Biomed Online. 2011;22:632โ646)
2 The Working Group on the update of the ESHRE/ALPHA Istanbul Consensus , Giovanni Coticchio, Aisling Ahlstrรถm, Gemma Arroyo, Basak Balaban, Alison Campbell, Maria Josรฉ De Los Santos, Thomas Ebner, David K Gardner, Borut Kovaฤiฤ, Kersti Lundin, M Cristina Magli, Saria Mcheik, Dean E Morbeck, Laura Rienzi, Ioannis Sfontouris, Nathalie Vermeulen, Mina Alikani, The Istanbul consensus update: a revised ESHRE/ALPHA consensus on oocyte and embryo static and dynamic morphological assessment,, Hum Reprod, 2025; https://doi.org/10.1093/humrep/deaf021 (in press)
3 The Working Group on the update of the ESHRE/ALPHA Istanbul Consensus , Giovanni Coticchio, Aisling Ahlstrรถm, Gemma Arroyo, Basak Balaban, Alison Campbell, Maria Josรฉ De Los Santos, Thomas Ebner, David K Gardner, Borut Kovaฤiฤ, Kersti Lundin, M Cristina Magli, Saria Mcheik, Dean E Morbeck, Laura Rienzi, Ioannis Sfontouris, Nathalie Vermeulen, Mina Alikani, The Istanbul Consensus update: a revised ESHRE/ALPHA consensus on oocyte and embryo static and dynamic morphological assessment. Reprod Biomed Online. 2025; https://doi.org/10.1016/j.rbmo.2025.104955 (in press)
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