Embryo grading is a process that evaluates the quality and development of embryos during IVF treatment in order to determine their health and likelihood of successful implantation.
What is Embryo Grading in IVF?
Embryo grading is a process used in in-vitro fertilization (IVF) to evaluate the quality of embryos before they are transferred to the woman’s uterus. Embryo grading is typically performed on the third day after fertilization, when embryos have developed to the 6-8 cell stage, or on the fifth or sixth day after fertilization, when embryos have developed to the blastocyst stage.
During embryo grading, embryologists examine the size, shape, and symmetry of the cells, as well as the presence and quality of certain structures within the embryo, such as the zona pellucida (the protective outer layer of the embryo) and the blastocoel (the fluid-filled cavity within the embryo).
Based on these criteria, embryos are assigned a grade or score that reflects their quality and likelihood of implantation and subsequent development into a healthy pregnancy.
The grading system varies between clinics and embryologists, but generally, embryos are graded on a scale of 1 to 4, with 1 being the highest quality and 4 being the lowest. Embryos with the highest quality grades are typically selected for transfer to the woman’s uterus, with the goal of improving the chances of a successful pregnancy. However, it’s important to note that embryo grading is not a perfect predictor of success, and some lower-quality embryos may still result in a healthy pregnancy.
Embryo Grading Process
During the process of Embryo Implantation in IVF, the embryos are cultured for around six days and during that period they receive quality grades every day.
Egg Retrieval and Insemination Day 0
The maturity of the egg is important as a mature egg has the best chance of getting fertilized. The three different stages of egg maturation are:
- Germinal vesicle (GV): It is the stage where the egg has not begun meiosis till now and is thus considered immature.
- Metaphase I (MI): This is the first phase of the egg is meiosis, but is not completely mature yet as it has not entered the second phase of meiosis. This type of immature egg matures after being in temperature-controlled incubation for a couple of hours.
- Metaphase II (MII): This is the second phase of meiosis of the egg, which is mature by now. Eggs at this stage are ready for fertilization and have the following characteristics.
- Clear cytoplasm/normal shape
- Single differentiated polar body
- Thin/clear zona pellucid
Fragmented/abnormal polar body
- Slightly pigmented/amorphous zona
- Fragmented/abnormal polar body
- Slightly pigmented/amorphous zona
- Cytoplasmic bodies
- PV debris
- Dark/grainy cytoplasm/misshapen
- >1 polar body structure
- Pigmented/thickened zona
Fertilization Check Day One
Fertilization can be seen clearly after 16 to 22 hours after the process of insemination. Normal fertilization can be seen by exactly two pronuclei in the center of a one-celled zygote. Fertilization is not abnormal when there is a single pronucleus and when there are more than two pronuclei present.
Multicell Grading Day Two/Three
On day two the single-cell zygote should divide into an embryo (approx. two to four cells). On day three the embryo should continue to divide (four to eight cells).
Good: have a clear cytoplasm with symmetrical cells
Fair: these cells are slightly asymmetrical having slight cytoplasmic irregularities
Poor: these cells are quite asymmetrical and might have grainy and dark cytoplasm
A = No fragmentation
B = <10% fragmentation
C = 10-35% fragmentation
D = >35% fragmentation
On the 4th day, the transition of embryos begins from a multi-cell embryo to a highly advanced developmental stage. Embryos then start compacting and forming morulae. Cells of a morula-stage embryo are not quite distinct like the previous days, and hence these embryos fail to receive quality grades.
Day Five/Six Blastocyst Stage
A blastocyst is a developed embryo that comprises two different cell types: one group of cells is referred to as the inner cell mass, which forms the fetal tissue, and another group of cells, known as the trophectoderm, helps in the formation of the placenta. Blastocysts are graded on the basis of their expansion (early, expanding, expanded, and hatching) as well as on the basis of the quality of these two different cell types (graded on a good-fair-poor scale). Blastocysts that are good or even fair in quality can be frozen.
Importance of Embryo Grading
Embryo grading is an essential process in the field of assisted reproductive technology (ART) where embryos are evaluated based on their quality and developmental stage. Here are some reasons why embryo grading is important:
Selection of the best embryos: Embryo grading allows embryologists to select the best embryos for transfer or cryopreservation. The grading system takes into account various factors such as the number of cells, cell symmetry, fragmentation, and degree of compaction. By selecting the best quality embryos, the chances of a successful pregnancy and live birth are increased.
Optimization of transfer timing: Embryo grading also helps to determine the optimal time for embryo transfer. Embryos are typically transferred into the uterus at a specific developmental stage, and grading can help ensure that embryos are transferred at the right time for the highest chance of success.
Cost-effectiveness: Embryo grading can be cost-effective because it allows embryologists to identify the most viable embryos for transfer, reducing the need for multiple rounds of IVF or other ART procedures.
Ethical considerations: Embryo grading can help to reduce the number of embryos that are discarded, as only the best quality embryos are selected for transfer or cryopreservation. This can be an important consideration for couples who may have ethical or religious objections to discarding unused embryos.
Embryo grading is an important tool in the field of ART that can increase the chances of a successful pregnancy and live birth, optimize the timing of embryo transfer, reduce costs, and address ethical concerns related to embryo selection.