Cryopreservation of ovarian tissue
Detailed information and a list of references can be found in Chapter 3.4of the FertiPROTEKT book, "Indications and fertility preservation methods for oncological and non-oncological disorders", which can be downloaded free of charge.
Ovarian tissue can also be frozen (cryopreserved) prior to chemotherapy and / or radiotherapy. Since the first births after ovarian tissue transplantation in 2004 worldwide and in 2008 in Germany, cryopreservation of tissue is an increasingly recommended technique for preserving fertility before chemotherapy. Currently, more than 73 live births known are known of worldwide and 16 in Germany (end of 2015).
Around 400 cryopreservations of ovarian tissue are performed each year, which currently corresponds to a total number of about 2500 cryopreservations. Of these, about 1450 are stored in the cryobank of the University Women's Hospital in Bonn, ca. 500 in the cryobank of the University Women's Hospital Erlangen, about 170 in the cryobank the University Women's Hospital in Innsbruck and about 100 in the cryobank the University Women's Hospital in Bern(November 2015).
After overcoming the primary cancer, the cryopreserved ovarian tissue can be thawed and transplanted in or on the remaining ovary or in a tissue pouch near the ovaries. A resumption of cyclic hormone production can be achieved in up to 63% of all patients who undergo transplantation of ovarian tissue according to a current register evaluation of the FertiPROTEKT network. Induction of puberty in patients where the tissue was removed for fertility preservation in prepubertal age has been described and is particularly emphasized as a special and unique feature of this fertility preservation method.
Removal, storage and transport of the removed tissue until preparation and cryopreservation
About 50% of an ovary is usually removed by laparoscopy under short general anaesthesia and immediately placed into the prepared transport medium.
If cryopreservation cannot be performed immediately at the removal site, there is the possibility of cooperating with specialized, external cryobanks (e.g. University Women's Hospitals in Bonn, Erlangen, Innsbruck and Bern). Transport takes place directly after surgical removal in special transport containers. The transport conditions include a time limit of 22 ± 2 hours which should not be exceeded and constant cooling at 4 to 8 ° C, which is guaranteed by special ice packs and transport containers. Several publications have shown that this method is fully functioning and also apparently causes no adverse effects in terms of tissue viability and the success rate after transplantation.
Cryopreservation of the prepared ovarian tissue
Using computer-controlled slow freezing, the samples are cooled in such a way that they can then be stored indefinitely n liquid nitrogen (- 196 ° C).
In addition to slow freezing, there is another method called vitrification (ultra-fast freezing). Both methods are used worldwide. However a thorough literature review showed that all births so far (except for one) solely result from the slow freezing method.
Which patients benefit from this technique?
Cryopreservation of ovarian cortex is recommended for women where the functional integrity of the ovaries is at direct or indirect risk as a result of oncological, haematological or other underlying disease. This is applies especially for imminent gonadotoxic chemotherapy or radiotherapy to the pelvic area. Prepubertal patients should also be considered, in whom the use of conventional assisted reproduction techniques (stimulation / freezing of oocytes) is not possible. The conditions in young postpubertal patients under 27 years of age are ideal are because the ovaries regularly release many egg cells during this time (embedded in primordial follicles) and the chances of fertility preservation after successful transplantation are therefore good. The FertiPROTEKT network recommends 35 as the upper age limit; however this limit is flexible in individual cases, depending on the ovarian reserve (AMH, antral follicle count).