C-16: Human oocyte cryopreservation: Current status and outlook

Abstract

Human oocyte cryopreservation is desired to preserve future fertility of young cancer patients, delay childbearing years, and avoid legal and ethical issues associated with embryo freezing. Unlike embryo freezing, oocyte cryopreservation has proved to be challenging due to susceptibility of oocytes to various cryoinjuries such as intracellular ice formation, disruption of cytoskeleton and spindle microtubules, premature exocytosis of cortical granules and zona hardening, parthenogenetic activation, and polyploidy. Although the first successful cryopreservation of human oocytes was reported in 1986, it took a decade of research and the use intracytoplasmic sperm injection to partially address some of the cryoinjuries and reproduce the initial success of human oocyte cryopreservation. Even then, the overall success rates were low and usually around 1–5%. These initial studies used slow cooling protocols. The first successful vitrification of human oocytes was achieved in 1999 with an overall success rate of ∼6%. Since then, considerably better results have been reported using both slow cooling and vitrification protocols. While the overall success rate after slow cooling still remains significantly lower than that of unfrozen controls, some fertility centers reported fertilization and pregnancy rates comparable to in vitro fertilization cycles using fresh oocytes after a vitrification approach that uses a minimal sample volume (