The cryopreservation of eggs entails some risks which, in the worst case scenario, can lead to the non-recovery and death of these reproductive cells. These risks are more common in the slow freezing method than in vitrification due to the reasons discussed below:
- Cooling between 15 and -5 °C is a critical point at which cell damage begins to occur. The membrane lipids and microtubules of the meiotic spindle are mainly affected.
- Between -5 and -80 °C, ice crystals may form that damage the structure of the cell membrane and compromise the viability of the egg.
- Between -50 and -150 °C, the solidification of the medium can damage the egg by cryopracture, with the pellucid zone being particularly affected.
- Excessive dehydration of the egg increases the concentration of solutes and the risk of irreversible collapse, which would be lethal to the cell.