The developmental potential of mature oocytes derived from rescue in vitro maturation

Objective: To examine the developmental competence of immature oocytes in stimulated cycles, that matured after rescue in vitro maturation (IVM) compared with their sibling in vivo matured oocytes. Design: Retrospective cohort study.Setting: IVF clinic.Patients: A total of 182 patients underwent 200 controlled ovarian stimulation cycles with intracytoplasmic sperm injection cycles in which immature oocytes were retrieved and at least one mature oocyte was obtained through rescue IVM.Intervention: In vitro culture of immature germinal vesicle (GV) and metaphase I (MI) oocytes, retrieved in stimulated cycles.Main Outcome Measures: Fertilization rate, cleavage rate, blastulation rate, ploidy of embryos evaluated using preimplantation genetic testing for aneuploidy, morphokinetic parameters and pregnancy outcomes.Results: In total, 2,288 oocytes were retrieved from 200 cycles. After denudation, 1,056 of the oocytes (46% +/- 16%) were classified as metaphase II (MII). A total of 333/375 (89%) of MI oocytes and 292/540 (54%) of GV oocytes matured overnight and underwent intra-cytoplasmic sperm injection. The fertilization rates of matured oocytes from MI rescue IVM (R-MI) and from GV rescue IVM (R-GV) were comparable with those of their sibling MII oocytes (71% vs. 66%; 66% vs. 63%, respectively). Early cleavage rates (80% +/- 35% vs. 92% +/- 20%; 80%+/- 42% vs. 95% +/- 28%, respectively) and blastulation rates (32 +/- 40% vs. 62 +/- 33%; 24 +/- 37% vs. 60 +/- 35%, respectively) were significantly decreased in rescue IVM matured oocytes (R-oocytes)-derived zygotes, but the blastocyst (BL) euploidy rate and good qualityBL rate were comparable with those of MII sibling-derived embryos. In addition, rescue IVM embryos showed significantly higher levels of multinucleation at the 2-and 4-cell stages, as well as higher rates of zygote direct cleavage from one to 3 to 4 cells. Overall, 21 transfers of rescue IVM embryos resulted in 3 healthy live births. Conclusions: For patients with a low maturation rate and/or low numbers of mature oocytes at retrieval, rescue IVM may contribute more competent oocytes and additional viable BLs for transfer from the same stimulation cycle, maximizing the chances for pregnancy and live birth. (Fertil Steril (R) 2023;120:860-9. (c) 2023 by American Society for Reproductive Medicine.)

Automated summary

The study compares the developmental competence of immature oocytes matured through in vitro rescue maturation (IVM) and their siblings matured in vivo. The results show that the fertilization rates of IVM-matured oocytes are comparable to their in vivo matured counterparts, but the cleavage and blastulation rates are lower. IVM embryos exhibit some developmental abnormalities but can still result in healthy live births.