Embryo Grading and Development

Grading of an embryo refers to the appearance of the tissue. Embryologists and physicians use embryo grading during IVF treatment to determine which embryos to transfer as well as the number of embryos transferred.

An embryo’s grade is not the only thing taken into consideration when having an embryo transfer. The patients age and fertility history are also taken into account.

Please note: The day of your egg retrieval counts as day 0.

Helpful Definitions:

Fragmentation: process where portions of the embryos cells have broken off and are now separated from the nucleated portion of the cell. fragmentation is common however, embryos with greater fragmentation may be less likely to progress through normal blastocyst development and then implant in the uterine wall to result in pregnancy.

Normal progression of embryo development: the rate at which your viable genetic material (eggs or embryos) taper off once they are in the embryology lab and growing. There are three main stages of this. The first phase is at the egg retrieval. Your doctor will retrieve all the follicles that they can, however, not all of them may contain mature eggs. The second phase happens with fertilization. Not all of the mature eggs will progress to become fertilized embryos. This happens with both conventional insemination and Intracytoplasmic Sperm Injection (ICSI). Phase 3 occurs with embryo growth, from day 3-6, and possibly 7, in some instances. Some embryos will not mature fully into a blastocyst, and stop gradually developing. These steps are all part of the IVF process and are to be expected when having an IVF treatment plan.

• Conventional Insemination: the mature egg is surrounded by a deposit of sperm in a petri dish and the sperm naturally find their way to the egg to fertilize. This mimics natural selection in a laboratory setting

• Intracytoplasmic Sperm Injection (ICSI): the embryologist selects a single sperm and manually injects it into the egg to fertilize.

Day 3 Embryo Grading

Embryos are graded A, B, and C on day 3.

• The grading for this stage consists of the number of cells an embryo has, followed by the quality of the embryo
• typically 6-8 cells are inside the embryo on day 3

Grade A

Embryos show that there are 6-8 evenly sized cells with no or less than 10% fragmentation

Grade B

Embryos have more irregularity in cells with 25-50% fragmentation

Grade C

embryos show 50% or more fragmentation

Blastocyst Grading

Blastocysts are graded on day 5, 6, and possibly day 7 based on progression.

The grading for this stage consists first of how far in development the blastocyst is. In the early blastocysts, a small fluid cavity forms. as the blastocyst develops, this cavity gets larger, and the outside shell of the embryo thins until the cells begin to herniate through the shell. This herniation allows implantation to occur.

• Embryos are first labeled early blastocyst (EB), then, as they progress through time they are called blastocyst (B), late blastocyst (B+), expanded blastocyst (XB), hatching blastocyst (HB) to finally a fully hatched blastocyst (HdB)

Labeled Blastocyst

A quality grade is given for both the inner cell mass and the trophectoderm.

• The first letter denotes the inner cell mass quality, the second letter denotes the trophectoderm quality
  • the inner cell mass is graded based on how many cells there are as well as how tightly packed the cells are spaced
  • the trophectoderm is graded based on the how many cells make up the cell’s border as well as their uniformity
• Blastocysts are graded as good (G), fair (F), or poor (P) for each of these factors

Example: a hatching blastocyst (HB) with good inner cell mass and trophectoderm quality would be labeled “HBGG“