#170 : Case Report: Live Birth Following Frozen Embryo Transfer of a Day 7 Euploid Blastocyst Derived from Vitrified-Warmed Oocytes with Delayed Maturation

Abstract

Background and Aims: A 35-year-old patient with secondary infertility underwent oocyte freezing at Alpha IVF in January 2021. She had 13 oocytes retrieved, of which, only 3 were mature and vitrified on Day 0 (Day0-MII) while the remaining 10 immature oocytes were left to mature overnight. On the following day, 8 mature oocytes (Day1-MII) were vitrified. This case report describes a live birth following frozen embryo transfer (FET) of a Day 7 euploid blastocyst derived from vitrified-warmed Day1-MII oocytes. Method: All of the patient’s MII oocytes were vitrified and warmed using Cryotec method (Cryotech, Japan). The oocytes were inseminated using PIEZO-ICSI (Japan) and were cultured up to 7 days. Usable blastocysts (with at least a Gardner’s score of BB) had their trophectoderm biopsied and subsequently vitrified. Biopsied cells were subjected to preimplantation genetic testing-aneuploidy (PGT-A) using next generation sequencing (Ion Torrent, USA). Finally, a euploid blastocyst was warmed and transferred. Results: Of the 11 vitrified MII oocytes, 10 survived post-warmed and 7 fertilized post-insemination: 2 from Day0-MII oocytes; 5 from Day1-MII oocytes. After 7 days of culture, none of the vitrified-warmed Day0-MII oocytes became usable blastocysts. Out of the 5 fertilised Day1-MII oocytes, 2 developed into usable blastocysts (1 day 6 blastocyst; 1 day 7 blastocyst) and were subjected to PGT-A and vitrification. Of the 2 blastocysts analysed, only the day 7 blastocyst was a euploid. Subsequently, this blastocyst was warmed and transferred in June 2022 which led to a clinical pregnancy. In February 2023, the patient underwent an uneventful delivery at 38 weeks of pregnancy. Conclusion: This case report demonstrated that a day 7 blastocyst derived from vitrified-warmed Day1-MII oocytes can result in a healthy live birth. We advocate that the salvaging of immature oocytes on Day 0 should be practiced.