Overview of IVF technology

Abstract: This article introduces the similarities and differences of four generations of in vitro fertilization (IVF) technology, including in vitro fertilization (IVF) combined with embryo implantation, intracytoplasmic sperm microinjection (ICSI), genetic diagnosis before embryo transfer, and plasma exchange technology, from the perspectives of implementation scope and benefits analysis. It helps readers understand the origin and development of IVF technology.

Introduction

Infertility is a global issue that affects family and social harmony, with approximately 10% -20% of couples of childbearing age worldwide suffering from different types of infertility. IVF technology has provided the possibility for many infertile patients to conceive new lives, and now IVF technology is becoming increasingly popular in China. In vitro fertilization (IVF) technology refers to the use of test tubes or culture media instead of the fallopian tubes to provide a place for the fertilization process, hence the name "IVF". At present, in vitro fertilization technology has developed to the fourth generation, but there is no relationship between the new generation replacing the old generation, but each generation of technology is dedicated to solving different fertility problems. So, patients can choose different IVF techniques based on their own situation to achieve their reproductive goals.

The Origin of IVF Technology

The world's first test tube baby was born in 1978 by British doctor Robert Edwards. But as early as 1962, Chinese biologist Zhang Mingjue had already completed the in vitro fertilization process of mammals using rabbits as the experimental subjects. Inspired by this experiment, Robert Edwards began to continue experiments with other animals [2] and achieved a series of successes, which prompted him to attempt human in vitro fertilization experiments and develop the first generation of in vitro fertilization technology based on it. In 2010, Robert Edwards was awarded the Nobel Prize in Physiology or Medicine for his research, and the technology of in vitro fertilization was recognized.

The Development History of IVF Technology

3.1 First generation IVF technology, also known as in vitro fertilization and embryo transfer (IVF-ET), can be roughly summarized into the following five steps: superovulation, collection of sperm and eggs, external fertilization, in vitro culture of embryos, and embryo transfer to the uterus for further development. The world's first test tube baby's initial oocytes were collected during the natural ovulation cycle, but natural ovulation has many drawbacks [3], such as fewer eggs being harvested and difficulty in collecting due to inaccurate ovulation cycles caused by physiological or psychological reasons of the patient. Therefore, later people often used drugs to stimulate ovarian superovulation in order to break through the limitations of the natural cycle and obtain more eggs, thereby improving the success rate of in vitro fertilization. After collecting sperm and eggs, it is necessary to incubate them for different durations before in vitro fertilization, depending on their maturity, in order to improve fertilization and cleavage rates. In vitro fertilization needs to be carried out in a simulated fallopian tube environment in a test tube or culture medium. After fertilization, the fertilized egg needs to be cultured in a test tube for a period of time. Generally, embryo transfer can be carried out when the fertilized egg divides into 2 to 4 cells.

The first generation of in vitro fertilization technology mainly solved the problem of organic infertility caused by female fallopian tube blockage, endometriosis, and polycystic ovary syndrome. As of 2012, hundreds of thousands of such test tube babies have been successfully born worldwide, and the success rate of IVF-ET has also increased to an impressive 50%. It is worth noting that the success rate will decrease with the age of women [4]

The technology of the first generation of IVF is not perfect. Although superovulation increases the number of eggs collected, it will increase the rate of multiple pregnancies. For pregnant women, it is easy to cause postpartum hemorrhage, pregnancy, diabetes and other complications. From the perspective of the fetus, it will lead to the decline of the survival rate of the fetus, the increase of the mortality rate and the teratogenicity rate to varying degrees. At the social level, the population growth rate may be accelerated, and the economic burden of the family will increase, which will inevitably affect the education of the next generation, Further leading to a decline in population quality. The occurrence of multiple pregnancies can be reduced through fetal reduction surgery, but it still cannot avoid the risks inherent in the procedure. The implementation of fetal reduction surgery may also affect the development of remaining fetuses, and even lead to the failure of in vitro fertilization. In addition, the first generation of in vitro fertilization technology has high requirements for sperm quality, which cannot meet the needs of patients with low sperm quality.

3.2 The second-generation IVF technology, also known as intracytoplasmic sperm injection (ICSI), is dedicated to overcoming male reproductive disorders. This technology is based on the first generation of in vitro fertilization technology, with the main difference being the method of in vitro fertilization. The second generation of in vitro fertilization technology requires fixing mature egg cells under a microscope, and then using a micro sampler to puncture the egg cell membrane to release sperm into the cytoplasm of the egg. This means that artificial injection is used instead of natural combination of sperm and egg, which can overcome reproductive problems caused by poor quality, insufficient quantity, or obstructive azoospermia of male sperm, while avoiding the occurrence of polyspermy. The intracytoplasmic sperm injection technology has solved the problem of natural fertilization failure and improved the success rate of IVF-ET, which is a milestone for infertile male populations. But the main problem with this technology is that, due to skipping the competitive process required for sperm egg fusion, fertilized eggs formed by sperm fusion without natural selection may pass on bad genes to the next generation. In order to solve this problem, the sperm hyaluronic acid binding assay (PICSI) was derived. This technology is to place sperm and hyaluronic acid hydrogel droplets on culture M together, and select sperm combined with the droplets as the material of test tube babies.

Since hyaluronic acid is the main component of the egg cell gel layer, sperm that can actively combine with microdrops will be more healthy and mature. Research has shown that the abortion rate of PICSI is significantly lower compared to ICSI, but there is no significant difference between the two in terms of live birth rate at term

In addition, the microinjection operation injects exogenous substances into the egg cell, which can cause varying degrees of damage to the cell structure such as the spindle due to the level of operation technology, affecting the differentiation and development of subsequent embryos [S]. It can be seen that the second-generation IVF technology still has shortcomings in ensuring embryo quality.

3.3 The third-generation IVF technology greatly increases the probability of offspring deformities or congenital foolishness for couples with severe genetic diseases or chromosomal abnormalities. In order to address these issues, the third generation of in vitro fertilization (IVF) technology, namely pre implantation genetic diagnosis (PGD) technology, has emerged based on assisted reproductive methods. PGD technology is based on modern molecular biology principles, using genome amplification and in situ hybridization techniques to perform genetic analysis on embryos obtained from in vitro fertilization, and to achieve quality inspection of embryos before implantation. PGD technology is mainly divided into two steps: live tissue examination and genetic diagnosis. Live tissue examination refers to taking the trophoblast cells of polar bodies, blastomeres, or blastocysts as embryonic representatives, waiting for genetic diagnosis. Genetic diagnostic methods mainly include polymerase chain reaction (PCR) and related technologies_ Fluorescence in situ hybridization (FISH) whole genome amplification (WGA) microarray comparative genomic hybridization (array CGH) single nucleotide polymorphism microarray (SNP array) and next-generation sequencing technology (NGS), etc. These technologies each have their own advantages. They are suitable for detecting different types of genetic diseases, such as PCR and its related technologies, WGA technology for the diagnosis of single gene genetic diseases, FISH technology array CGH for the diagnosis of chromosomal abnormalities, and SNP array and NGS technology for the diagnosis of the above two types of genetic diseases. The advantages of PGD technology are mainly reflected in: D can control genetic diseases in the early embryonic stage, avoiding pregnant women from discovering problematic fetuses during pregnancy and having to undergo unintended abortion; 2 can avoid implementing fetal reduction surgery. In previous assisted reproductive processes, it was usually necessary to perform embryo reduction surgery during pregnancy to select the best developing embryo, while PGD technology can pre select the "best embryo" for transplantation in vitro to avoid the use of post pregnancy embryo reduction surgery, which is more in line with the basic principles of ethics; PGD technology can prevent early prenatal examinations such as amniocentesis and fetal umbilical cord puncture from causing bleeding and uterine infections. PGD technology has made significant achievements in helping couples with severe genetic diseases, elderly women, etc. obtain healthy fetuses. Currently, PGD technology can screen for more than 100 common genetic diseases. Experiments have shown that there is no statistically significant difference in the incidence of morphological abnormalities such as organ damage or atypical hyperplasia between children screened with PGD technology and those naturally conceived [6]. Middleburg et al. [7] found that these children did not show significant differences in developmental indicators such as mental and neurological development and behavioral psychology, but the optimal neurological score for children screened with PGD technology was slightly lower.

Of course, there are also some issues with the clinical application of PGD technology. Firstly, there may be misdiagnosis during genetic testing of embryos, and PGD technology cannot provide absolute assurance for the quality of embryos; Secondly, by continuously improving genetic technology, it is possible for humans to selectively reproduce offspring by screening so-called "excellent" genes at the time, making gene types tend to be singular. Over time, this will inevitably reduce the diversity of human genes, thereby affecting the direction and speed of human evolution. In addition, can further development of PCD technology use gene editing technology to modify genes of embryos with certain genetic defects? These are obviously issues that require serious consideration by humanity.

3.4 The fourth generation IVF technology is known as germ plasma transfer (GVT) technology. The main method of this technology is to first obtain the nucleus of a female egg and transplant it into high-quality enucleated egg cells, so that the two can reorganize into a more dynamic egg cell. The recombinant egg cells are fertilized in vitro to form an embryo, then transplanted into the mother's uterus and complete subsequent development.

This technology is mainly suitable for older women with poor egg quality or young women with aging eggs. This group of women still have ovulation function, but due to poor health or old age, low egg vitality often occurs, such as unfertilized eggs or abnormal cell division after repeated fertilization. It is usually difficult to obtain normal embryos using previous IVF techniques. By replacing the nucleus with high-quality eggs, the chances of conception for older women can be significantly improved. In theory, as long as women have the ability to ovulate, their reproductive age will no longer be limited. The problem with the fourth generation of in vitro fertilization technology is that although the genes carried by recombinant eggs mainly come from the nucleus of the egg, and the genetic genes in the cytoplasm account for less than 1%, we still cannot ignore its existence, which makes the genes of the fetus actually come from the "third parent". In addition to poor egg quality and low vitality, the physical condition of the elderly mother who provides the nucleus of the egg is often not suitable for pregnancy, resulting in a "surrogate" mother, These situations can lead to complex social, ethical, moral, and legal issues that are difficult to deal with: there may be multiple fathers and mothers within a family, and even a baby can have up to four mothers, including a genetic mother who provides the nucleus of the egg, a mother who provides the cytoplasm of the egg, a surrogate mother, and a caring mother. This presents a new challenge for families currently linked by blood ties and families as a unit of society. Based on this, the Chinese government has explicitly prohibited the use of egg plasma replacement technology.

4 Conclusion

Looking back at the development process of over 40 years, in vitro fertilization technology has emerged and gradually developed amidst huge controversies. From the first generation to the fourth generation, breakthroughs have been made for different reproductive difficulties, expanding the scope of application of human assisted reproductive technology, benefiting thousands of households and gaining widespread recognition from society. It has brought hope for many infertile couples to enjoy family happiness, making diseases and age no longer obstacles to reproduction, Promoted the eugenics and nurturing of humanity.

References

Zhao Ping's Nobel Prize in Physiology discusses in vitro fertilization technology [J]. Biology Bulletin 2012, 47 (1): 61-62