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Feasibility of Injecting Immature M1 Oocytes in Terms of Blastocyst and Euploidy Rates

Authors: Haley N Teets, B.S., Khalied Kaskar, H.C.L.D, PH.D., Matthew VerMilyea, H.C.L.D, PH.D., and Kaylen Silverberg, M.D.

OBJECTIVE: Many human embryology laboratories only perform ICSI on oocytes that morphologically indicate maturity based on the presence of a polar body (MII) and not immature (MI) oocytes. Labs that inject MI oocytes are doing so as a last resort for possible fertilization as this requires additional time and resources. The additional time needed to inject MIs may delay injected MII oocytes from being placed back in the incubator and therefore could cause potential deterioration. The literature does not strongly support whether injecting MI oocytes produces more usable euploid blastocysts. The aim of this study was to determine if ICSI of MI oocytes is feasible in obtaining euploid blastocysts.

MATERIALS AND METHODS: A total of 533 patients undergoing IVF with ICSI were included in this retrospective study. Immature oocytes (MI) were injected with sperm and cultured until Day 7 and evaluated for fertilization and blastocyst development. Blastocysts were biopsied and tested for euploidy using PGT screening.

RESULTS: A total of 982 MI oocytes were injected of which 309 showed normal fertilization with 2 pronuclei (2pn) (31.5%), 12 with 1 pronucleus (1.2%), 38 with ≥3 pronuclei (3.9%) and 623 with no fertilization (63.4%). Of the 2pn’s, 31 blastocysts were formed (10.0%) of which 13 were on Day 5 (4.2%), 16 on Day 6 (5.2%) and 2 on Day 7 (0.6%). 29 blastocysts were biopsied for PGT and 12 were deemed euploid (41.4%), 12 aneuploid (41.4%), 4 mosaic (13.8%) and 1 with no result (3.4%).

CONCLUSIONS: Injecting MI oocytes proves to have very low euploid blastocyst development (1.2%). The additional time and resources taken to inject MIs may not justify the low euploid outcome. More data is needed to determine if euploid embryos developed from injected MIs result in live births.

IMPACT STATEMENT: ICSI of immature MI oocytes may not be feasible as it yields low euploid blastocyst rates.

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