Cryopreservation aims at freezing living cells and storing them over a longer period without compromising their developmental potential. Particularly in the field of assisted reproductive technology, the optimum use of this freezing technique is critical to the success of fertility treatment.
In order to ensure both efficiency and safety of this technique, it needs great commitment and a genuine interest in science and research. This is impressively demonstrated by two current studies conducted by the
IVF Centers Prof. Zech.
The desire to have children and cryopreservation
Water is the basis of all life. There is no life without water – there is nothing really new about this wisdom. But water can also be hostile to life – i.e. when it freezes. This is about a very special scientific branch – cryonics or cryopreservation. Cryonics will play an ever-increasing role in the field of reproductive medicine.
For example as regards the so-called „Fertility Preservation“, which involves measures to preserve human fertility, i.e. prior to chemo or radiation therapy or if women/couples want to allow themselves more time before starting a family, this is when cryopreservation plays a key role. Please read in the following blog posts what this means in detail: “Precaution instead of worrying about the future” / “Having a career and children – you can do both”
The importance of freezing techniques becomes clear when, during IVF treatment, an appropriate build-up of the uterine lining (endometrium) could not be obtained through hormonal stimulation or when ovarian hyperstimulation syndrome (OHSS) has occurred. Thus, embryo transfer cannot take place and for the time being, the embryos will be cryopreserved. Additionally, the change in the transfer policy towards single embryo transfer (SET), the ongoing improvement of stimulation and culture protocols as well as the introduction of new, innovative techniques produces a growing number of good quality surplus embryos that are not transferred in a so-called fresh embryo transfer.
Cryopreservation – Freezing of:
Slow Freezing vs. Vitrification
Even though embryo freezing may sound rather simple at first, the practical application is extremely challenging! Here we come back to the role played by water. When water freezes, ice crystals start to form – and if this process takes places inside a cell, it usually means the end for the cell’s viability, since these ice crystals act like small but very sharp “razor blades” and may destroy important cell compartments. To avoid this, there are basically two different cryopreservation techniques: the so-called slow-freezing and the vitrification method.
Slow-freezing involves gradually lowering the temperature. Step by step water is removed from the cell while the ion concentration is increasing, thus preventing intracellular ice formation (inside the cell). This method entails extracellular ice formation (outside the cell). The procedure is not suitable for use in all the different stages of embryonic development.
Vitrification allows for avoiding both intra- as well as extracellular ice formation. With the help of special media and ultra-rapid cooling and thawing rates, cells are directly transferred from a liquid state into a glass-like solid condition. Although during the last years the vitrification technique has been able to establish itself as a highly efficient cryopreservation procedure, until recently there were still many unresolved issues. Apart from the concerns about the safety of the embryos when using the specialized highly viscous medium, it was still not completely clear as to how long vitrified embryos could be stored in liquid nitrogen or whether an extended storage period might impair their integrity.
At the IVF Centers Prof. Zech we have been successfully performing the technique of aseptic vitrification for years. This is precisely why we wanted to supply evidence that due to this technique, we are on the safe side. During the past half-year alone, we have published two scientific papers in the journal “Human Reproduction”, one of the world’s leading journals in the field of assisted reproductive medicine.
In the first study (Vanderzwalmen et al., 2013), we used a complex experimental set-up and investigated – in co-operation with CHIREC in Brussels and the GIGA Institute in Liège – the actual intracellular concentration of cryoprotectant in mouse embryos prior to vitrification. Subsequently, the results were compared to those obtained with the slow-freezing method. As it turned out, the intracellular concentration of cryoprotectants is, on the one hand, far lower than cryoprotectant levels in the media used for vitrification and, on the other hand, the concentration is significantly lower when compared to the slow-freezing technique (to get more details on the study, please click here).
Another study (Wirleitner et al., 2013) focused on the possible impact of storage time of vitrified embryos on their viability. Apart from the thawing rates, the study also included parameters such as pregnancy rates, babies born, the risk of premature birth, gender balance and birth weight. In this study it could be proven that storage times of up to 6 years (this is how long we have used the method at our centers) did not have any negative impact on the vitrified embryos.
Conclusion: Aseptic vitrification is a reliable technique enabling the safe cryostorage of embryos for a longer period of time, without impairing their developmental potential. In the light of our results, no evidence was found to substantiate the risk of increased malformation rates or other congenital anomalies (to get more details on the study, please click here).