Cryopreservation is a special procedure in which several kinds of cells and tissues can be kept for a long time for use at a later date. It involves freezing these tissues at -196°C and storing them in liquid nitrogen. The origin of the word ‘cryopreservation’ is the Greek word ‘kryos’, meaning ‘very cold’.
Cryopreservation is an accepted method in fertility treatments. In the Netherlands, fertility centres such as ours generally offer the cryopreservation and -storage of several types of materials:
When freezing unfertilized oocytes, we use a special freezing technique to minimalize the chances of damaging the oocytes. Unfertilized oocytes contain much more water than fertilized oocytes, and therefore they are much more vulnerable while going through the cryopreservation process. Water crystals may develop during the freezing process and will cause more damage in unfertilized oocytes. However, when employing the vitrification technique, nearly all oocytes will survive the freezing process.
Since 2016, we’ve been freezing embryos during their blastocyst process, which means five days after the oocyte retrieval. Over 95% of all blastocysts that are put into cryopreservation storage survive the freezing and subsequent thawing processes.
Sperm cells are eligible to be put into cryopreservation storage if there is a real risk of damaging the sperm cells in a treatment, such as with the use of some medications. We also offer the possibility of freezing sperm cells when undergoing a sterilisation surgery, in case of the lengthy absence of a partner or if the man in question has issues with sperm production. When using donor sperm, the donor sperm will be frozen before it is eligible to be used in a fertilization treatment. After checking the donor extensively for any infections at the time of donating, the sperm will be declared eligible for use. Sperm quality will often be decreased by some time in cryopreservation storage.
In case of an IVF/ICSI treatment
It makes sense to freeze high-quality leftover embryos that developed during an IVF or ICSI treatment so that they can be used for another treatment at a later date. These embryos can be thawed and used later, such as if the parents decide that they want a second child. This procedure is also referred to as cryotransfer, embryo transfer or embryo replacement. The advantage of cryopreservation, in this case, is that the mother won’t have to go through hormone stimulation and an oocyte retrieval for a second time.
When treating severe diseases
The treatment of certain severe diseases carries a real risk of infertility in the patient. Examples are the treatment of cancer by way of chemotherapy, radiation or surgery. People suffering from such diseases who have a desire to have children can, after talking it through with a physician and estimating their personal risk of infertility, decide to freeze their sperm, testicular tissue, oocytes or ovarian tissue before starting said treatment – as a precaution.
Many young women do have a desire to have children, but can’t or won’t become pregnant for personal reasons at that time in their lives. For example, they might want to focus on their career or find the right partner. In the Netherlands, these women may freeze their oocytes so that they can use them later, and still have relatively young oocytes to work with. This would increase their chances of a successful pregnancy at a later age.
When someone wishes to use a frozen, fertilized oocyte to possibly facilitate a pregnancy, this oocyte can be thawed and placed in the hopeful mother’s uterus at the right moment of her menstrual cycle. This is also called a cryotransfer. Unfertilized oocytes which have been put into cryopreservation storage will first be fertilized using an intracytoplasmic sperm injection (ICSI).
In case of a perfect, regular menstrual cycle, a cryotransfer can be performed in the hopeful mother’s natural cycle. Another possibility is to support the formation of the endometrium using estrogens in order to prepare it as much as possible for the lodging of the oocyte. Your treating nurse or physician will be able to monitor the thickness of the endometrium using an ultrasound.
When it’s thick enough, the hormone progesterone will be administered, simulating ovulation. This changes the structure or the endometrium, preparing it for the reception of one of multiple embryos. A third option is to stimulate with hormones clomifene or FSH, which both support follicle maturation before the embryo transfer. After that, your treating nurse or physician can insert the embryo(s) into the uterus through a flexible catheter.
Cryopreservation has been a commonplace procedure for many years, and most research supports the notion that it doesn’t cause any negative effects. Of course, personal advice from a physician tailored to your situation should always be considered in your treatment.