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Blastocyst vitrification is standard in assisted reproduction, but clinical data on ultra-rapid vitrification are limited. This pilot study evaluates the safety, feasibility, and preliminary clinical performance of an ultra-rapid blastocyst vitrification protocol compared with the standard approach.
Blastocyst cryopreservation by vitrification is currently the standard approach in assisted reproductive technology, providing high post-warming survival rates and clinical outcomes comparable to those of fresh embryo transfer. Ongoing refinements of vitrification techniques aim to further improve laboratory efficiency and workflow while maintaining biological safety and clinical effectiveness.
Ultra-rapid vitrification protocols have been developed to shorten equilibration times by modifying exposure kinetics to cryoprotectants, while preserving the fundamental biophysical principles of vitrification. Although ultra-rapid warming protocols are well established, clinical data specifically evaluating ultra-rapid vitrification of blastocysts remain limited.
Moreover, ultra-rapid vitrification requires mechanical collapse of the blastocyst before cooling, introducing an additional embryological manipulation with potential biological implications that warrant careful clinical validation. In this context, the present pilot study aims to evaluate the safety, feasibility, and preliminary clinical performance of ultra-rapid blastocyst vitrification compared with the standard vitrification protocol, prior to broader clinical implementation.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Standard Vitrification Protocol | Active Comparator | The standard vitrification protocol corresponds to the routine clinical practice of the laboratory and consists of the following steps:
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| Ultra-Rapid Vitrification Protocol | Experimental | The ultra-rapid vitrification protocol is identical to the standard protocol in terms of media, devices, and laboratory conditions, with the following modifications: Preparation step - Blastocyst shrinkage: Prior to equilibration, artificial collapse of the blastocyst is performed using a single laser pulse to induce blastocoel shrinkage. The subsequent steps are: 1. Equilibration step: Blastocysts are equilibrated in Equilibration Solution (ES) for 2-4 minutes. Vitrification solution exposure: Transfer to Vitrification Solution (VS) for a maximum of 90 seconds. 3. Loading: Loading of the blastocyst onto a Cryotop device. 4. Vitrification: Immediate plunging of the Cryotop into liquid nitrogen within 1 second. 5. Capping: Immediate capping under liquid nitrogen. |
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| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Standard Vitrification | Other |
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| Measure | Description | Time Frame |
|---|---|---|
| Post-warming survival rate | the proportion of vitrified blastocysts that remain morphologically viable after warming, expressed as a percentage of all warmed blastocysts. | Immediately after warming (within the same laboratory session) |
| Clinical pregnancy rate per transfer (only first transfer will be considered). | defined as the proportion of embryo transfers resulting in a clinical pregnancy, confirmed by the presence of an intrauterine gestational sac on ultrasound. Only the first embryo transfer per patient is included in the analysis. | 6-8 weeks after embryo transfer |
| Measure | Description | Time Frame |
|---|---|---|
| Blastocyst re-expansion | defined as the resumption of blastocoel expansion after warming, as assessed by partial or complete reformation of the blastocyst cavity, indicating post-warming viability | Within 2 hours after warming |
| Post-warming blastocyst morphokinetic parameters |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Monica Parriego, PhD | Contact | 0034932274700 | monpar@dexeus.com | |
| Ignacio RodrÃguez, MSc | Contact | 0034932274700 | 22029 | nacrod@dexeus.com |
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| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Hospital Universitario Quiron Dexeus | Not yet recruiting | Barcelona | 08028 | Spain |
| PubMed Identifier | Type | Citation | Retractions |
|---|---|---|---|
| 31973647 | Background | Boyard J, Reignier A, Chtourou S, Lefebvre T, Barriere P, Freour T. Should artificial shrinkage be performed prior to blastocyst vitrification? A systematic review of the literature and meta-analysis. Hum Fertil (Camb). 2022 Feb;25(1):24-32. doi: 10.1080/14647273.2019.1701205. Epub 2020 Jan 24. | |
| 36410446 | Background |
| Label | URL |
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| Related Info | View source |
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| ID | Term |
|---|---|
| D007246 | Infertility |
| ID | Term |
|---|---|
| D000091662 | Genital Diseases |
| D000091642 | Urogenital Diseases |
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| Ultra-Rapid Vitrification | Other | The ultra-rapid vitrification protocol is identical to the standard protocol in terms of media, devices, and laboratory conditions, with the following modifications: Preparation step - Blastocyst shrinkage: Prior to equilibration, artificial collapse of the blastocyst is performed using a single laser pulse to induce blastocoel shrinkage. The subsequent steps are:
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Assessment of post-warming embryo developmental dynamics based on time-lapse observation. Morphokinetic parameters will include time to blastocoel re-expansion and time to resumption of blastocyst development, measured in hours from warming to embryo transfer. |
| From embryo warming until embryo transfer (within 2-6 hours post-warming) |
| Post-warming blastocyst morphological quality | Evaluation of blastocyst morphological quality after warming and prior to embryo transfer. Blastocysts will be graded according to standard morphological criteria based on blastocoel expansion, inner cell mass quality, and trophectoderm appearance. Results will be reported as the proportion of embryos achieving good-quality blastocyst grade per standard scoring system. | From embryo warming until embryo transfer (within 2-6 hours post-warming) |
| Technical or embryological adverse events. | defined as any unexpected or unfavorable technical or laboratory-related events occurring during blastocyst warming, handling, culture, or preparation for transfer, including damage to the embryo, procedural errors, or protocol deviations that may affect embryo viability. | From blastocyst warming until embryo transfer, within the same clinical procedure (up to 6 hours post-warming) |
| Hospital Universitario Quiron Dexeus | Recruiting | Barcelona | 08028 | Spain |
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| George JS, Keefe KW. Freezer burn or learning curve? Prolonged time since blastocyst vitrification and impact on pregnancy outcomes. Fertil Steril. 2023 Jan;119(1):45-46. doi: 10.1016/j.fertnstert.2022.11.017. Epub 2022 Nov 19. No abstract available. |
| 41686351 | Background | Gunst J, Joris H, Vynck M, Godderis K, Vercammen M, Roggeman S, van de Vijver A. Validation and clinical study of single-step vitrification combined with single-step warming of human blastocysts. J Assist Reprod Genet. 2026 Mar;43(3):837-850. doi: 10.1007/s10815-025-03790-1. Epub 2026 Feb 13. |
| 35963753 | Background | Kovacic B, Taborin M, Vlaisavljevic V, Reljic M, Knez J. To collapse or not to collapse blastocysts before vitrification? A matched case-control study on single vitrified-warmed blastocyst transfers. Reprod Biomed Online. 2022 Oct;45(4):669-678. doi: 10.1016/j.rbmo.2022.03.030. Epub 2022 Apr 10. |
| 25316444 | Background | Li Z, Wang YA, Ledger W, Edgar DH, Sullivan EA. Clinical outcomes following cryopreservation of blastocysts by vitrification or slow freezing: a population-based cohort study. Hum Reprod. 2014 Dec;29(12):2794-801. doi: 10.1093/humrep/deu246. Epub 2014 Oct 14. |
| 40479947 | Background | Martinez-Rodero I, Gallardo M, Pisaturo V, Scarica C, Conaghan J, Liebermann J, Cuevas-Saiz I. Shorter protocols for vitrification and post-warming dilution of human oocytes and embryos: a narrative review. Reprod Biomed Online. 2025 Aug;51(2):104857. doi: 10.1016/j.rbmo.2025.104857. Epub 2025 Feb 7. |
| 37801195 | Background | Perez-Sanchez M, Pardinas ML, Diez-Juan A, Quinonero A, Dominguez F, Martin A, Vidal C, Beltran D, Mifsud A, Mercader A, Pellicer A, Cobo A, de Los Santos MJ. The effect of vitrification on blastocyst mitochondrial DNA dynamics and gene expression profiles. J Assist Reprod Genet. 2023 Nov;40(11):2577-2589. doi: 10.1007/s10815-023-02952-3. Epub 2023 Oct 6. |
| 27827818 | Background | Rienzi L, Gracia C, Maggiulli R, LaBarbera AR, Kaser DJ, Ubaldi FM, Vanderpoel S, Racowsky C. Oocyte, embryo and blastocyst cryopreservation in ART: systematic review and meta-analysis comparing slow-freezing versus vitrification to produce evidence for the development of global guidance. Hum Reprod Update. 2017 Mar 1;23(2):139-155. doi: 10.1093/humupd/dmw038. |
| 38827525 | Background | Sciorio R, Tramontano L, Campos G, Greco PF, Mondrone G, Surbone A, Greco E, Talevi R, Pluchino N, Fleming S. Vitrification of human blastocysts for couples undergoing assisted reproduction: an updated review. Front Cell Dev Biol. 2024 May 17;12:1398049. doi: 10.3389/fcell.2024.1398049. eCollection 2024. |
| 29706285 | Background | Sekhon L, Lee JA, Flisser E, Copperman AB, Stein D. Blastocyst vitrification, cryostorage and warming does not affect live birth rate, infant birth weight or timing of delivery. Reprod Biomed Online. 2018 Jul;37(1):33-42. doi: 10.1016/j.rbmo.2018.03.023. Epub 2018 Apr 21. |
| 26364080 | Background | Van Landuyt L, Polyzos NP, De Munck N, Blockeel C, Van de Velde H, Verheyen G. A prospective randomized controlled trial investigating the effect of artificial shrinkage (collapse) on the implantation potential of vitrified blastocysts. Hum Reprod. 2015 Nov;30(11):2509-18. doi: 10.1093/humrep/dev218. Epub 2015 Sep 12. |