In order to increase the success rates in in vitro fertilization (IVF), new techniques, methodical and more efficient approaches are needed beyond preimplantation genetic screening (PGS). A new approach could be the characterization of the proteome of embryos during the IVF process. This means that specific proteins secreted by the embryo in the surrounding growth medium can be analyzed and compared between embryos to identify potential markers for successful embryo transfer and ultimately pregnancy.
This procedure can result in understanding the processes during the entire incubation period from the moment of oocyte fertilization to embryo transfer, and then analyzing the culture medium used in the multi-culture medium exchange during the cultivation period. This procedure of embryo transfer to a new culture medium is essential for embryo development and is performed daily, or at least when the embryos reach the embryoblast stage on day 4. Media remaining after embryo removal is routinely discarded. However, this medium can still be useful for a detailed analysis of proteins and lipids secreted by the embryo during the previous incubation process and can help gain insight into the current developmental state of the embryos.
The European Association of Human Reproduction and Embryology (ESHRE) report from February 2018 shows that Europe continues to lead the world with around 50% of all reported in vitro fertilization (IVF) cycles. The latest figures are available for 2014, showing that 39 European countries reported about 800,000 cycles comparing 150,000 cycles in the USA or 65,000 in Australia and New Zealand.
Although there are no official reports from China, this country is estimated to have performed more than 800,000 IVF cycles with a growth trend. In summary, ESHRE estimates that around 2.5 million IVF cycles are performed each year and about 500,000 babies are born following IVF. The pregnancy rate depends on embryo quality, and in 2014 the average pregnancy rate per embryo transfer in Europe was 35% after IVF, 33% after ICSI, 30% after frozen embryo transfer, and 59% after egg donation. Younger patients (<35 years) appear to have higher pregnancy rates.
There are large variations between countries in terms of the number of embryos transferred and multiple births that can occur following multiple embryo transfer. Multiple pregnancies are classified as high risk pregnancies and pose a significant health risk to both mother and baby. However, regardless of this, the application of multiple embryo transfer still exists and is widely used to increase the chance of pregnancy. Currently, efforts are being made to reduce the number of multiple embryo transfers, with an average of 1.81 embryos per transfer reported.
In Europe, the rate of multiple births for embryo transfers dropped from 26.9% in 2000 to 17.5% in 2014 (latest data available), and is expected to fall further, according to the European Association of Human Reproduction and Embryology report. Some countries, such as Sweden, have achieved very low multiple birth rates, and a single embryo transfer was performed on more than two-thirds of all transfers.
The importance of IVF in society is also emphasized by the 2010 Nobel Prize awarded to Robert Edwards, who was with Robert Steptoe, who is considered to be the father of the Type baby method. The IVF process is extremely stressful, both physically and psychologically, both for the parents and mainly for the mother and mother. A number of physical examinations and medical procedures are performed to ensure that the process results in a successful pregnancy. In the IVF process, especially when deciding which embryo to transfer to keep the chance of success at the highest level, the best possible decision based on fast and accurate information about the state of the embryo is needed. A steady increase in pregnancies has been observed following artificial reproduction techniques (ART) such as IVF and intra-cytoplasmatic sperm injection (ICSI) due to the increase in the age of expectant mothers in the past years. The reasons for this development should be seen in economic, educational and social factors and this causes the rate of elderly patients to increase gradually. As age progresses, fertility and fertility decrease. However, advances in reproductive medicine may be one of the reasons why an increasing number of women are delaying childbearing.
Increasing pregnancy rates for IVF procedures is absolutely necessary to reduce the burden on patients and lower procedural costs. This should be repeated frequently until a pregnancy has been achieved and the embryo has reached a successful delivery. There is a need for new technologies and methods that are more efficient than the current approach using PGS. A new approach could be the analysis of the proteome of embryos during the IVF process. This means analyzing specific proteins secreted by the embryo in the IVF surrounding the culture medium. Routinely, the media remaining after embryo transfer is discarded. The multiple embryo transfer that occurs during the IVF procedure is required after the fertilization stage, and the spent media is a rich source of biological material that can be used for diagnostic purposes.
The medium can be useful for a detailed study of proteins and lipids secreted by the embryo at all stages of development and can be used for estimation of “embryo quality” and selection of corresponding embryos for primary transfer. An overview of the technologies and approaches used and a simplified experimental approach is provided. The method used in laboratories is used as an example of the technologies used, and a number of different approaches can be discussed.
Proteomics is a promising technology for identification and validation of possible biomarkers for embryo selection in ART. As listed by Dyrlund et al., A growing list of secreted proteins has been identified that could contribute further to this field. However, the challenge of research still involves the reliable and reproducible identification of a proteomic secretome signature. This signature should be directly related to the viability of the embryo and the success of the procedure, that is, successful pregnancy and the birth of the child. This is a very challenging task, not only because of the complexity, heterogeneity and diversity of human embryos, but also because of the non-reproducibility of the culture media used and the contaminating proteins in them.
Another challenge in clinical use of proteomic methods is the speed of proteomic analysis. Sample preparation, measurement, and data analysis of a sample within the time frame required for IVF are currently not possible. Current sample analysis methods require at least half a day for the fastest proteomic method available, which is very long. However, proteomic methods, once clinically validated, can contribute to the identification and validation of putative biomarkers that can be analyzed using other, faster methods by generating the corresponding antibodies.
Writer: Ozlem Guvenc Agaoglu