Prior to chemotherapy and/or radiotherapy, eggs, fertilized or mostly unfertilized, can be frozen (cryopreserved). Cryopreservation of fertilized and unfertilized eggs is an established technique that can also be used for the purpose of fertility preservation in patients prior to cytotoxic therapy.
Two different procedures are used, the slow freezing procedure or vitrification, an ultra-fast freezing procedure.
In order to cryopreserve sufficient fertilized or/and unfertilized eggs, ovarian hyperstimulation is required. This can start independently of the respective cycle day, but requires about two weeks. The number of eggs obtained may depend on pre-existing diseases and the age of the woman.
Freezing of unfertilized eggs is an established technique and does not affect chromosomal disorders (disorders of the genetic material). However, it should be noted that with increasing age the number and quality of eggs decreases.
Later, the unfertilized eggs can be thawed as part of fertility treatment, but only intracytoplasmic sperm injection (ICSI) can be used, since the cumulus cells that surround the egg and needed for in vitro fertilization (IVF) were removed before the freezing process.
Not only unfertilized, but also fertilized eggs can be cryopreserved. Freezing of fertilized eggs is an established technique worldwide and has been used for decades.
The survival rates of both unfertilized and fertilized eggs are very good, the freeze-thaw methods are safe and not associated with major risks.