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.

Detailed inform­a­tion and a bib­li­o­graphy can be found in the Fer­ti­PRO­TEKT booklet “Indika­tion und Durch­führung fer­til­ität­s­pro­tekt­iver Maßnahmen bei onko­lo­gis­chen und nicht-onko­lo­gis­chen Erkrankun­gen”, 2nd revised edition 2020, which was written by members of the Fer­ti­PRO­TEKT Netzwerk e.V. and is available free of charge (in German).

(Chap. 3.2)

An english version can be bought: Fertility Pre­ser­va­tion in Onco­lo­gic­al and Non-Onco­lo­gic­al Diseases a practical guide by Michael von Wolff & Frank Nawroth ISBN 978–3‑030–47567‑3 from

Part III.II page 179ff