Cryopreservation and cryotransfer: procedure and costs

Why cryopreservation?

If a natural desire to have children remains unfulfilled for a long time, many couples resort to the possibility of artificial insemination. However, the Embryo Protection Act stipulates that a maximum of three fertilized egg cells may be implanted in a patient within a treatment cycle. If more than three suitable oocytes have emerged from the preparatory puncture of the ovaries, there is the possibility of freezing them using cryopreservation in order to save them for a possible later transfer.

What is cryopreservation?

The word cryo comes from the Greek and means cold. Cryopreservation is the freezing of cells in liquid nitrogen so that they can be used again at a later point in time. This process is not directly a method of artificial insemination , but rather a special component or a kind of support within reproductive medicine.

For the purpose of artificial insemination, both excess fertilized egg cells and sperm can be frozen. The preservation of sperm is particularly useful if the sperm were obtained from a testicular biopsy by MESA or TESE. It is also possible to freeze sperm as a precautionary measure, for example before radiation treatment for cancer that could result in infertility. Egg freezing is usually a lot more complicated.

What happens during the cryopreservation of oocytes?

The Embryo Protection Act stipulates that a maximum of three embryos may be placed in the uterus of a patient undergoing artificial insemination. However, as it is not uncommon for more than three egg cells to be obtained during the preparatory follicle puncture, these can be frozen for as long as desired in order to use them for a further treatment cycle in the event of failed implantation. For this purpose, the oocytes are preserved in liquid nitrogen at -196°C. Three factors are of particular relevance:

• Fertilized egg cells: As a rule, only egg cells that have already been fertilized are frozen. Unfertilized egg cells are rarely viable after thawing.
• Freezing in the pronucleus stage: Although the egg cells should be fertilized before freezing, their development must not be too advanced. According to the Embryo Protection Act, fertilized egg cells may only be preserved in the pronuclear stage, since the cells are not yet an embryo at this point.
• Freezing of at least 3 oocytes: Cryopreservation of oocytes is only usual if there are at least three excess oocytes. The survival and development rate of the preserved oocytes is around 70 percent after thawing, which is why the effort involved in preserving only one or two oocytes would hardly be worthwhile, since the chances of success for a pregnancy that occurs are then too low.

How does the cryotransfer work?

After the egg cells have been thawed, they can be implanted in the patient after the first cell division, i.e. as an embryo, using IVF or ICSI , for example . This is referred to as the so-called cryotransfer. Whether the embryo implants itself in the uterus and thus a pregnancy occurs depends to a large extent on the condition of the uterine lining at the time of the transfer. There are three ways to optimally prepare the uterine lining and thus the return of the embryo.

• Natural menstrual cycle: With a regular menstrual cycle and a natural structure of the uterine lining, no special measures are necessary to prepare the body for receiving the embryo. However, it is possible to induce ovulation artificially in order to better coordinate the timing of the individual steps of artificial insemination.
• Hormonal stimulation: If the patient has an irregular menstrual cycle, it is possible to use special hormonal stimulation to promote the growth of the lining of the uterus and ensure ovulation.
• Estrogens and corpus luteum hormones: With this method, optimal conditions for implantation are created by administering two different hormones. First of all, the uterine lining is built up by taking estrogens, for example through tablets or vaginal suppositories. The development is monitored by ultrasound. At the appropriate time, ovulation is simulated by administering progesterone, the so-called corpus luteum hormone. As a result, the structure of the mucous membrane changes in such a way that it is ready to receive the embryo, even though no ovulation has actually taken place.

What are the advantages and disadvantages of a cryotransfer?

Cryotransfer is a patient-friendly method, as the woman only has to go through the cumbersome egg cell retrieval and pre-treatment once and can still go through several treatment cycles if necessary. The pregnancy rate per puncture therefore increases thanks to cryopreservation. Egg cells can also be stored for any length of time, which makes it much easier to coordinate the various preparatory steps involved in artificial insemination.

A clear disadvantage of the method of cryotransfer is that the chances of a pregnancy occurring after fertilization with previously frozen oocytes are only about half as great as with a return with “fresh” oocytes. The costs for the preservation and the subsequent transfer are also not covered by health insurance.

Whether cryopreservation makes sense for a couple depends on the respective personal situation and the medical history of both partners. An intensive consultation with the doctor treating you or, if necessary, an expert is therefore highly recommended in order to be able to use the method promisingly and to avoid unnecessary strain.