Evaluation of embryo quality after defrosting

This article is professionally consulted by Master, Doctor Nguyen Thi Cam Van - IVF Lab Doctor - Reproductive Support Center - Vinmec Times City International Hospital.

With advances in assisted reproductive technology, the ability to freeze embryos for storage has become increasingly popular and offers many benefits. Evaluation of embryo quality after thawing is one of the important factors that help bring about a successful IVF cycle. So what is the evaluation of embryo quality after thawing?

Embryo quality assessment is a job of embryologists. Based on the embryo characteristics to score the quality of the embryo created or after thawing.
All embryo classification systems are subjective. Although we can make estimates based on scientific evidence and on the experience of many embryologists who classify millions of embryos to predict their potential, there are many cases where embryos Poor scores produce pregnancy, while perfect embryos fail to end up producing pregnancy. Also, regardless of the embryo classification and evaluation system, it doesn't tell us what's going on inside the embryo genetically.

Thanks to advances in assisted reproductive technology, the quantity and quality of embryos are increasingly improved. The patient will have a chance to get pregnant many times but only need to aspirate eggs and create embryos once thanks to embryo cryopreservation.
Embryo freezing is done based on the principle of replacing water in the cells with frozen preservatives. The embryo is then cooled down to -196°C in liquid nitrogen. The embryo's metabolic and developmental activities are stopped. When the patient wants to get pregnant, the embryo will be thawed and transferred into the woman's body.
Many of the studies that have been performed to compare frozen and fresh embryo transfers in women have not shown any significant difference in pregnancy success rates. Embryo cryopreservation as well as embryo thawing will help infertile couples have a cycle of IVF when transferring stored embryos.

There are different embryo scoring systems for day 3 and day 5 embryos. Embryologists use a grading system to help determine which embryos need to be transferred or frozen. Usually, embryo transfer will take place with 3-day or 5-day embryos. Because embryos develop differently these days, we have different classification systems for day 3 embryos (cleavage stage) and day 5 embryos (blastocyst stage).
3.1. Classification of Day 3 Embryos Day 3 embryos are called “separation stage” embryos. The reason for this designation is that the cells in the embryo are dividing (or dividing) but the embryo itself is not growing in size.
Conceptually you would think that embryos would divide in a very specific sequence, one cell becoming two, two cells becoming four, four cells becoming eight and so on. However, the actual embryos do not divide synchronously. We usually see three, five, six cell embryos, etc. This is not a sign of a poor embryo, but rather one that is developing normally. Also, when the embryo divides, sometimes a small part of the cytoplasm (inside the cell) breaks off and forms a band that we call fragmentation. The fragments do not contain a nucleus and are not considered to be cells. The cause of fragmentation is not well understood, but embryos containing a lot of fragmentation are at a developmental disadvantage.
The cleavage stage embryos are classified based on 2 criteria: the number of cells in the embryo and their appearance under a high-powered microscope. Normally, a well-developed, well-developed day 3 embryo will contain between 6 and 10 cells. From studies performed in the laboratory and from other published studies, we know that embryos containing this number of cells are more likely to develop into viable blastocysts than embryos with a low number of cells. more cells.
Embryo quality is a morphological assessment of the cells in the embryo. For example, a type one embryo is one in which all the cells are the same size and there is no fragmentation in the embryo. The system that embryologists use to assess the appearance of embryos is presented in the following.
Description of bar stock
Class 1 embryos of equal size; no fragmentation was found in the same size Class 2 embryos; only minor fragmentation Class 3 embryos of unequal size; not fragmented to moderately fragmented Embryo type 4 cells of equal or unequal size; moderate to severe fragmentation Type 1 to 2 embryos appear to have the greatest potential to progress to the blastocyst stage. However, type 3 embryos can also be of good quality if the appearance can be explained by asynchronous cell division rather than by poor development. Scientists have published data showing that cell count in day 3 embryos is a better indicator of potency than an embryo's quality score. Therefore, type 3 8-cell embryos will have better potential than 4-cell type 2 embryos on day 3.

3.2 Sorting Day 5 Embryos On day 5, the embryo is continuing to divide and the number of cells continues to increase, but the cells are also developing and differentiating into specific cell types. By this time, the embryos should have begun to develop extra space within the zona pellucida (ZP or “shell”) that surrounds the embryo. They begin to expand and thin the ZP in preparation for the developmental stage when the blastocyst ruptures through this membrane (“hatched”) in preparation for implantation into the uterine lining.
There are two types of cells in day 5 embryos or blastocysts. A cell type that forms the embryonic bud cell mass (ICM). This mass of cells will eventually develop into a fetus. The cell mass surrounding the ICM is the trophoblast (TE). These cells will continue to make necessary tissues during pregnancy (such as the placenta). This cell type together forms a fluid-filled sphere with TE cells on the outside and ICMs on the inside. Like balloons, if you pop a balloon and put a ping pong ball inside, that's the shape of a blastocyst. The shell of the balloon is TE and that of the ping pong ball is ICM. Both of these cell types are needed to create a healthy pregnancy. So when classifying embryos at the blastocyst stage, the embryologist evaluates the letter grade for each cell type as well as for the fluid-filled cavity or blastocyst. The embryologist also assigns a grade to designate the degree of expansion of the embryo (this relates to the size of the embryo as well as how many cells are contained in the embryo). Examples of levels of expansion are:
Very early blastocyst, where the cavity has just begun to form in the embryo and has not yet differentiated the expanded blastocyst cell types, in which the cavity is fully formed, the embryo contains 100 to 125 cells, but still contained in a thin ZP extruded Blastocyst, where the embryo is outside the ZP and contains up to 150 cells. Here are some examples of embryos that we normally see on day 5.
As you can see from the examples above, blastocyst classification is very complex and there is no absolute score. Although A is "better" than D, for example, an embryo with a class D ICM may still be developing, and in later review the ICM may have been compacted into a B or even A. In addition, the Expansion level is an indicator of the developing embryo. Many times a Blastocyst very early on day 5 becomes an expanded Blastocyst on day 6 and can be frozen if other indicators are good. The determination of whether an embryo has good potential is made by taking into account all components of the embryo.
Workpiece classification is a tool. This is a tool that doctors and embryologists use together with the patient's age, fertility, and other information to determine the optimal embryo transfer date, the appropriate number of embryos to transfer, and the correct which embryos need to be transferred.
Currently, the Center for Reproductive Support - Vinmec Times City International General Hospital has performed embryo freezing using a new technique of vitrification. The outstanding advantage of this method of embryo freezing is that the freezing time is fast, the embryo survival rate after thawing is over 95%, the pregnancy rate from embryo freezing is 50%, almost double the old methods. . Embryos that undergo vitrification have no intracellular ice crystal formation (while the slow cooling method can lead to ice crystals inside when lowered from -50 to -150 degrees Celsius – this is the main cause of the problem). major cause of membrane rupture or cell rupture).
Therefore, with the technique of freezing embryos by vitrification, embryos are protected more safely, when thawed, they will have a high survival rate. This is one of the safe and highly effective methods today, used in cryopreservation of embryos as well as eggs and sperm.
Therefore, the method of embryo freezing using the new technique of vitrification is currently the solution chosen by many couples to help bring about great opportunities in parenting.