Oocyte cryopreservation outcomes including pre-cryopreservation and post-thaw meiotic spindle evaluation following slow cooling and vitrification of human oocytes

Abstract

Objective: To report our oocyte cryopreservation (OC) outcomes including meiotic spindle (MS) evaluation of metaphase II (MII) oocytes destined for OC and thaw.

Design: Retrospective.

Setting: University-based infertility center.

Patient(s): Women attempting pregnancy using cryopreserved oocytes.

Intervention(s): OC, MS evaluation.

Main outcome measure(s): Survival, two pronuclear (2PN) fertilization, achieving embryo quality suitable for transfer or refreezing, blastocyst formation.

Result(s): Thirty-two OC-thaw cycles resulted in 20 pregnancies, 18 either ongoing or delivered. In 26 cycles, MS evaluation was performed: 262/303 (86%) thawed/recovered oocytes survived, 218/262 (83%) achieved 2PN fertilization, 133/218 (61%) became suitable for day-3 and 122/218 (56%) for day-5 transfer. In total, 58 embryos were transferred resulting in a 62% pregnancy and a 41% implantation rate. Of oocytes evaluated before cryopreservation, 247 (82%) were spindle-positive; 96% of these were also spindle-positive after thawing. Blastocyst formation and suitability for day-5 transfer was achieved more often if a post-thaw spindle was visualized. Of all slow-cooled and vitrified oocytes, a higher percentage of those slow-cooled achieved 2PN fertilization and usability. MS evaluation of oocytes cryopreserved by either method was associated with similar outcomes.

Conclusion(s): OC outcomes are improving. An MS was almost always exhibited both before cryopreservation and after thawing, suggesting that, with appropriate technique, OC presents minimal harm to the MII oocyte. A meiotic spindle evaluation might help to further OC technology.