Embryo Grading Improves Your IVF Success
Embryo grading is a detailed evaluation process that assesses the quality and developmental potential of embryos created during in vitro fertilization (IVF). Our skilled embryologists employ specific criteria to assign grades based on the appearance and developmental stage of each embryo.
Embryo grading plays a pivotal role in the success of IVF. Understanding the science behind embryo grading can empower patients with valuable insights into the potential of each embryo.
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Day of egg retrieval
After an egg retrieval, our embryologist follows an embryo through its developmental stages.
- Approximately 3 to 4 hours after an egg retrieval, the lab team examines the eggs to assess if the egg is mature. If the egg is not mature it cannot be fertilized. On average, 70 percent of all retrieved eggs are mature.
After an initial assessment, we inseminate all mature eggs in one of two ways:
- Intracytoplasmic sperm injection (ICSI) – A procedure in which one sperm cell is injected into an egg—the most common form of insemination, as it gives embryologists the most control over the insemination process.
- Conventional insemination – A procedure that places the egg into a culture medium containing between 5,000 and 10,000 sperm to facilitate fertilization. Immature eggs are routinely added into the insemination medium in this process, because they have the potential to mature during incubation overnight.
After insemination, our lab team places eggs into the incubator to begin their development.
Day 1
After retrieval, eggs will remain in the incubator for 15 to 18 hours after the insemination procedure. An embryologist will then remove the eggs to determine if normal fertilization has occurred.
On average, 70percent of all inseminated eggs will fertilize.
When we check for fertilization, we will also perform a basic chromosomal assessment. We expect to see two pronuclei in the center of the embryo, which, at this stage, is called a zygote. One of these pronuclei will be from the sperm and the other from the egg, and they represent each half of the chromosomes provided by the sperm and egg.
The presence of two pronuclei within the cell tells us that fertilization occured normally . Anything more or less than two pronuclei indicates a chromosomal abnormality that prevents the embryo from use.
All normally fertilized embryos will then go back into the incubator where they will remain between checks until they are transferred or frozen.
Day 2 – 4
On days 2 – 4 after retrieval, the embryos remain in the incubator. They are not checked because it is best to leave embryos as undisturbed as possible.
Day 5
On day 5 after retrieval, the embryo ideally develops into a blastocyst, consisting of about 150 cells.
This stage is the first time we see the cells begin to organize themselves. Cells divide into two groups:
- Inner cell mass – The group of cells that will become the embryo.
- Trophectoderm – The group of cells that will establish the embryos connection with the endometrium — the membrane that lines the uterus.
Once embryos reach this stage of development, they need to be placed into a uterus or be cryopreserved.
At Shady Grove Fertility, we commonly allow all embryos to develop for at least 5 days prior to transfer or cryopreservation, allowing us the opportunity to monitor embryo development closely and better predict the likelihood of a positive outcome.
Embryos can reach the blastocyst stage 5, 6, or 7 days days after egg retrieval. Blastocysts that form earlier (day 5 ) have higher implantation potential; and yet those embryos that take an extended period to become a blastocyst may still result in a healthy pregnancy.
While there is a correlation between slower embryo development and lesser viability;, we will generally freeze any embryo that reaches a high quality blastocyst stage by day 6 or 7 for future use if it is of adequate morphology.
Final embryo grading exam
We monitor all developing embryos and take notes as they move through the stages of their development. This documentation gives us a good idea as to the potential viability of the embryo. Before transfer or cryopreservation, however, we conduct one final assessment of the embryo.
During this process, we examine the cluster of inner cells and the outer trophectoderm, and then assign each part of the embryo a grade from A to C based on set criteria.
Inner Cell Mass
The inner cell mass receives a grade depending on how pronounced the cell number & size is:
- A – Pronounced inner cell mass
- B – Visible inner cell mass, but less pronounced
- C – Very low cell number in the inner-cell mass
Trophectoderm
The grade assigned to the outer trophectoderm layer is dependent upon how many cells it contains. The higher the number of cells, the higher the grade (A, B, or C) that is assigned.
In both cases, a grade of A is the target, as it suggests the highest likelihood of successful implantation. However, A and B grades can often be considered interchangeable given the relatively wide range of speed of development of each individual embryo — presence of a critical number of cells generally defined as grade B and above is adequate to indicate a significantly higher potential for implantation and healthy pregnancy.
The role of embryo grading in IVF success
Embryo grading aids our physicians and embryologists in selecting embryos for transfer. By assessing the development of embryos and assigning them a final rating, we provide patients with information needed to help make decisions as they progress through the IVF process. It is important to note that while embryo grading can help offer guidance, it is a subjective process. For the most reliable information on embryos, your physician may recommend preimplantation genetic testing.
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