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Study question Can human oocytes be cyropreserved when they were previously inseminated while obtaining normal fertilization, embryo development and pregnancies? Summary answer Cryopreservation of recently inseminated human oocytes produces normal 2PN zygotes, viable embryos and ongoing pregnancies. What is known already Oocyte vitrification is a well-established technique in the infertility field supported by its effectiveness to freeze and thaw embryos at various stages of development. However, it is yet unknown whether cryopreservation performed in a period between conventional in vitro insemination and the appearance of pronuclei, affects any of the steps leading to fertilization, thereby arresting this process. Study design, size, duration Case report that includes 5 IVF cycles where cryopreservation and thawing were performed in a pre-zygote stage, 4 hours after the conventional insemination of oocytes. The rationale for this procedure was to comply with a government restriction to circulate and work in order to prevent the spread of the SARS-CoV–2 virus, unexpectedly 3 days ahead (effective on 03/19/2020). Participants/materials, setting, methods: Off-site embryologists cancelled all pending embryo transfers and returned home (2,000 km away) before the stay-home quarantine. Five couples were informed and consent was obtained on the urgent need to cryopreserve their already inseminated oocytes despite of the limited scientific information. We vitrified 28 oocyte-sperm pairs in vitrification devices containing 2 to 3 inseminated oocytes each. Main results and the role of chance Eight months later all non-essential activities, including non-urgent procedures in hospital facilities, were permitted again, allowing embryologists to travel and resume their postponed work. We thawed 19 of the so-called “pre-zygotes” corresponding to 4 of the 5 initial couples. Female ages were 29, 39, 38 and 37 years old. Our primary outcomes were detection of pronuclei and the occurrence of fertilization. The secondary outcome was pregnancy success. On day 1, we observed the presence of 2PN in 16 oocytes (84%). Only one patient with 2 oocytes failed to fertilize. We transferred 2 good-to-fair-grade cleaved embryos to each of the 3 patients, obtaining one pregnancy with a positive fetal heartbeat from the 39 years old patient. Two of the couples were also able to cryopreserve 2 and 1 surplus embryos on day 5, respectively. Limitations, reasons for caution Our strategy was used exclusively to overcome an unexpected adverse event while complying with State and County regulations on COVID–19. As a case report, a large sample size is needed to confirm and extend these results including the putative detrimental effects of arresting the fertilization process through vitrification. Wider implications of the findings: Although cryopreservation implies to arrest of any stage of a development continuum, to the best of our knowledge, this is the first time that both fertilization and pregnancy were achieved after halting the fertilization process long before the appearance of pronuclei (at ∼4 hours after insemination). Trial registration number Not applicable

human reproduction

P–185 Overcoming a sudden COVID–19 lockdown and other similar unforeseen adverse events: Oocyte-sperm cryopreservation 4 hours after conventional in vitro insemination