Ultra-fast vitrification and rapid elution of human oocytes: Part II - verification of blastocyst development from mature oocytes.

Research question: Will ultra-fast vitrification (UFV) and rapid elution of mature human oocytes retain the reliable, high survival rates and meiotic spindle normality seen in the germinal vesicle model, and will these oocytes maintain their developmental competence to form blastocyst-stage embryos following artificial oocyte activation (AOA)?

Design: Conventional vitrification treatment was compared with UFV treatment in mature, germinal-vesicle-derived oocytes (Phase 2, Expt. 2, n = 50) and substandard donor oocytes, metaphase I-metaphase II (MII) oocytes and poor-quality MII oocytes (n = 222). Post-warming survival, the integrity of the meiotic spindle and AOA-related development were assessed.

Results: Overall survival rates were higher (P = 0.003) for UFV/rapid elution treatment (94-100%, mean = 98%) compared with conventional vitrification/control dilution treatment (80-90%, mean = 83.3%). MII oocytes derived from immature germinal vesicles following conventional vitrification/control dilution or UFV/rapid elution treatments proved to be capable of activated development (54-71% cleavage rate), with four blastocysts produced. AOA treatment with DMAP exposure yielded optimal activated development. When vitrifying mature oocytes, both UFV and conventional vitrification treatments exhibited normal activated development and blastocyst production (34.9% and 31.7%, respectively).

Conclusions: Considering that oocyte freezing was deemed non-experimental based primarily on healthy live births from frozen-oocyte-derived embryo transfer the validation of normal blastocyst formation using the novel UFV approach is a critical accomplishment. The UFV method for oocyte cryopreservation represents a strategic deviation from traditional semi-equilibration vitrification protocols. UFV is a more time-efficient approach that consistently yields a higher survival rate, and thus has the potential to create more embryos. These findings justify proceeding with strategic clinical trial applications.