Why do frozen embryos be transferred for embryo transfer?

For fresh embryos and frozen embryos, which kind of transplantation method will have a higher success rate?

This is one of the most frequently asked questions of prospective parents who do embryo transfer during the IVF cycle.

To tell the truth, when it comes to transplanting "frozen embryos," the first response most of us must draw is

"Fresh is better than frozen!"

"Why take it for freezing? It's not enough to transfer the embryos directly"

"Like the vegetables and fruits we eat every day, the frozen ones are definitely not as delicious and nutritious as the fresh ones!"

What about embryo transfer? Are fresh embryo transfers better than frozen embryos?

the answer is negative.

To be clear to everyone:

The implantation rate and live birth rate of frozen embryo transfer are significantly higher than that of fresh embryo transfer, and the incidence of abortion and early abortion of frozen embryo transfer fetus is significantly lower than that of fresh embryo transfer.

I believe that after reading this article, I can accurately solve all doubts of prospective parents.

XNUMX. Frozen embryos and embryo transfer

The embryos are finally stored in liquid nitrogen (-196°C) under vitrification and freezing conditions, and the embryos are in a "dormant" state. The activity of cellular enzymes in liquid nitrogen is almost completely suppressed. The intracellular water freezes to form glass-like ice, which effectively avoids the formation of intracellular ice crystals and dehydration of cells during freezing.

From a scientific perspective, the metabolism and molecular activities of frozen embryos are almost completely at rest at minus 196°C. Therefore, the length of storage has no significant impact on their developmental potential and health status.

In 1984, the first newborn born with freeze-thaw embryo transfer was born in Australia. Since then, frozen embryo transfer technology has become another milestone in assisted reproductive technology (ART).At present, there are 20 years of frozen embryos in the world, and there are cases of successful pregnancy.

American IVF technology often chooses to use blastocysts that develop to day 5-7 for transplantation. In theory, 99% of fertilized eggs can develop to the third day of morula stage, but only about 50% of them can continue to develop and become blastocysts. The success rate of IVF is directly related to embryo quality.

A common misunderstanding of prospective parents: To test the success rate of babies, they need to be transplanted as soon as the embryos form blastocysts.

Actually, this is not the case.

The European Society of Human Reproduction and Embryology (ESHRE) has also published a research report that suggests that if you want to maximize pregnancy success rate, fresh blastocyst transplantation may not be the best select.

XNUMX. The relationship between frozen embryo transfer and pregnancy rate

So, what are the advantages of frozen embryo transfer?

A team of professors from Miguel Angel Checa, Hospital Universitari del Mar, Spain, total633A comparative study was conducted on test-tube baby cycles.

Among them, 316 test-tube baby cycles were performed with fresh embryo transfer, while the remaining 317 cycles used frozen embryo transfer and were followed up to 24 weeks of pregnancy.

Statistics show thatThe success rate of frozen embryo transfer can reach 50%, while that of fresh embryo transfer is about 38%.In other words, the pregnancy success rate of frozen embryo transfer is 1.31 times that of fresh embryo pregnancy.

The results of this study objectively reflect the success rate of all age groups.

Statistics from multiple reproductive medicine centers around the world show that the rate of continued pregnancy at 24 weeks after frozen embryo transfer is 24% higher than that at 30 weeks after fresh embryo transfer.

Experts gave several explanations for the above phenomenon:

1. Choose the best uterine condition for transplantation.The DNA mutation rate in the endometrial tissue cells that promote the excretion cycle is very large; in addition, after the egg retrieval, the endometrial receptivity may decrease, or the endometrial thickness may be thin, and other diseases require nursing care.

Choosing a better endocrine and endometrial environment for embryo implantation can increase the embryo implantation rate and reduce the incidence of ectopic pregnancy.

2. Prevent ovarian hyperstimulation syndrome (OSHH).After the egg retrieval operation, the serum estrogen level is too high, and the expectant mother may develop ovarian hyperstimulation syndrome, which will also reduce the embryo implantation rate and increase the chance of fetal pregnancy.Frozen embryo transfer can reduce the impact of ovarian hyperstimulation syndrome.

3. Before transplantation, the embryos need to be genetically screened to select healthy embryos. The genetic screening will take about a week. During this period, embryo freezing is required.

4. In addition to the high success rate, frozen embryos can help save a lot of time and effort required for the synchronization cycle, and flexibly arrange the conception time. It is undoubtedly very beneficial for multinational customers who go to the United States for test tubes.

XNUMX. The relationship between frozen embryo transfer and premature infants and low birth weight neonates

In addition to Professor Checa's confirmation that frozen embryo transfer has improved pregnancy rates, there are earlier studies that have confirmed the relationship between frozen embryo transfer and preterm and low-birth-weight neonates.

At the Sahlgrenska University Hospital in Sweden, Dr. Ulla-Britt Wennerholm's team conducted a large data compilation of all IVF cycles in Denmark, Norway and Sweden from 1982 to 2007. They found:Newborns born after successful pregnancy through frozen embryo transfer have a higher incidence of premature babies, ultra-premature babies, low-birth-weight neonates, and ultra-low-birth-weight neonates than newborn babies born after successful embryo transfer To be low.