Vitrification of gametes, i.e. (from the Latin word vitrum, which means glass), is the process of freezing them so rapidly that the water doesn’t form ice crystals and solidify into a glass-like structure. This system is more efficient than “slow freezing” methods to preserve gametes for future cycles of ART. This was confirmed by a paper published by the GeneraLife team on the journal “Human Reproduction Update”. 

The principal finding of this systematic review and meta-analysis support vitrification as being superior to slow freezing for cryopreservation of both human oocytes and embryos in clinical ART. While the quality of the evidence for clinical outcomes comparing the two cryopreservation methods was mostly low and based on clinical pregnancy, rather than live births, that for post-thaw cryosurgical of oocytes and embryos was moderate. Due to the improved cryosurgical outcomes with vitrification many laboratories worldwide have completely replaced slow freezing with vitrification. It is there- fore unlikely that additional prospective comparisons with current protocols will be performed. The optimized oocyte/embryo/blastocyst cryosurgical rates and clinical outcomes achieved with the use of vitrification have important clinical implications, which together allow a personalized approach in the care of different patient populations. 

Cryopreservation is an essential component in the treatment of patients undergoing ART and should be optimized in every IVF laboratory – say the authors – as it allows for increased results and offers the possibility to reduce multiple gestations and hyperstimulation syndrome risk. According to the available evidence appraised in this systematic review and meta-analysis, vitrification is the best strategy for cryopreservation of all developmental stages from mature oocytes to embryos at the blastocyst stage. Furthermore, it allows for reliable segmentation of the IVF cycle by temporally disconnecting the stimulation process from embryo transfer; consequently, this affords additional time for new invasive and non-invasive methods of embryo selection. Finally, if standardized and/or automated, the consistency and efficiency of the technique would likely be assured across all laboratories.

Link: https://doi.org/10.1093/humupd/dmw038