A brief history of oocyte cryopreservation: Arguments and facts

Abstract

The term “cryopreservation” refers to the process of cooling cells and tissues and storing them at subzero temperatures in order to stop all biological activity and preserve their viability and physiological competences for future use. Cooling to subzero temperatures is not a physiological condition for human cells; this is probably due to the high content of water in the living matter, whose conversion to ice crystals may be associated with severe and irreversible damage. Among reproductive cells and tissues, metaphase II oocytes are notably vulnerable to cryopreservation, mainly because of their large size, low surface area to volume ratio, relatively high water content and presence of the meiotic spindle. As human biological systems lack efficient internal defense mechanisms against chilling injuries, it is of the utmost importance to supply adequate external support, in terms of cryoprotectant additives, appropriate cooling/warming rates, and suitable long‐term storage. Over the years, scientists have proposed different cryopreservation strategies in the effort to achieve an optimized recipe ensuring cell survival and, at the same time, maintenance of the physiological functions and abilities necessary to continue life. However, despite the first success obtained in the 1980s with frozen oocytes, it was not until recently that notable improvements in the cryopreservation technique, thanks to the advent of vitrification, allowed a breakthrough of this fine procedure.

Safety of Ovaleap® (Follitropin Alfa) in Infertile Women Undergoing Superovulation for Assisted Reproductive Technologies: A Multinational Comparative, Prospective Cohort Study

“…Thus, the conduct of a freeze all policy may suggest that the patient was at an increased risk for OHSS. However, the trend observed in women of reproductive age in recent years toward delaying childbearing and “social egg freezing” and the improvements achieved in the cryopreservation techniques may suggest that OHSS risk may not necessarily be the underlying factor ( 30 , 31 ). Indeed, in some fertility clinics, there is an increase in practice to conduct freeze-all procedures independently of OHSS risk.…”

DNA fragmentation index (DFI) as a measure of sperm quality and fertility in mice

“…Our results clearly show the importance of testing DNA quality to ensure delivery of an intact genetic payload to oocytes by natural fertilization, intrauterine insemination (IUI), IVF or ICSI. This is particularly emphasized in the case of human reproduction where ICSI is now a routine procedure 55,56 , since ICSI requires only one sperm for the procedure and sperm from infertile men usually have high DFI 57 . Given its relevance to fertility, we believe that DFI used as an assessment of DNA fragmentation should be included as part of sperm quality analysis in humans as well as in animals in order to diagnose infertility, improve outcomes using ARTs, predict fertility, select animals for ART, guide selection of an ART procedure, and increase reproductive success.…”

Oocyte Cryopreservation: Retrospective Analysis Of 5 Years Experience

“…A 30-yearold woman with 6 oocytes has a 24.1% chance of live birth when a 40-year-old woman with 6 oocytes has a 13.4% chance of live birth after vitrification (22). Female age is the main (23). The contribution of each oocyte dissolved after 41 years to the success of pregnancy decreases thoroughly (24,25).…”