This commentary has been compiled with the objective of sharing some facts and opinions regarding embryo grading and development. It is a question that often arises with recipients undergoing egg donation IVF, at that crucial embryo development stage before the embryo transfer.
Embryo “quality” as the embryologist see it under the microscope in the IVF lab, gives some reasonable ability to predict the chances for pregnancy after the embryo transfer procedure.
Most IVF clinics “grade” each embryo using one of many scoring systems. Unfortunately, there is no agreement at all as to which system to use.
Ultimately, the true test of embryo quality is whether it implants and develops normally and eventually goes home from the hospital with mom and dad. In other words, embryo-grading systems are imperfect, and we always need the pregnancy test, and the final pregnancy outcome, to tell us more about “embryo quality” than a microscope could ever reveal.
Embryos, depending on the stage of development, are most often graded given the following factors:
- Rate of cell division. An embryo that has seven, eight, or nine cells is more likely to implant than an embryo with either fewer or more cells. Then more than 10 is not a good sign. It means the embryos are developing faster than they should.
- Cell number. Embryos should be at 2 to 4 cells at 48 hours after egg retrieval and preferably about 7 to 10 cells by 72 hours.
- Cell regularity with symmetry in size and shape. An embryo that divides unevenly may not be up to standard.
- Fragmentation. The percentage of the embryo that has broken off into pieces during cell division. Anything with less than 20% fragmentation is a good embryo.
However, because there are many other contributing factors involved that we cannot see or measure, the generalisations about “quality” made from grading embryos are often inaccurate.
Embryo Grading Systems
Below: Picture of a high quality human blastocyst embryo 5 days after fertilization.
The clump of cells in the 10 to 12 o’clock area is the inner cell mass (ICM) which become the fetus.
The trophectoderm cells (TE) that will form the placenta surround the fluid cavity
The fluid-filled blastocoel cavity is in the center. Courtesy of http://www.advancedfertility.com.
It is VERY important to note that different clinics, within South Africa and the world, apply different protocols for embryo grading. The below is just to give you an INDICATION of how a grading system may be applied to stages of embryo development.
The Gardner blastocyst grading system assigns 3 separate quality scores to each blastocyst embryo:
- Blastocyst development stage – expansion and hatching status
- Inner cell mass (ICM) score, or quality
- Trophectoderm (TE) score, or quality
|Blastocyst development and stage status|
|1||Blastocoel cavity less than half the volume of the embryo|
|2||Blastocoel cavity more than half the volume of the embryo|
|3||Full blastocyst, cavity completely filling the embryo|
|4||Expanded blastocyst, cavity larger than the embry, thinning of shell|
|5||Hatching out of the shell|
|6||Hatched out of the shell|
|ICM Grade||Inner cell mass quality|
|A||Many cells, tightly packed|
|B||Several cells, loosely grouped|
|Very few cells|
|TE Grade||Trophocteoderm quality|
|A||Many cells forming a cohesive layer|
|B||Few cells, forming a loose epithelium|
We see some cycles fail after transferring 3 perfect looking embryos, and we also see beautiful babies born after transferring only one “low grade” embryo. The true genetic potential of the embryo to continue normal development is impossible to measure accurately with current technology. Hopefully, future advances will give us better insight.
It is also important to note that embryos that were given a “low grade” by the embryologist do not result in a problem with the baby. As far as we know, the children born from low-grade embryos are just as cute, intelligent, strong, etc. as those born from high-grade embryos. The only difference seems to be with the chance for the embryo(s) to result in a pregnancy.
The doctors can never tell from what a embryo looks like, whether they will implant or not. There was a patient that had 4 embryos transferred – 2 were graded as good and 2 were very poor graded embryos. All 4 implanted and she gave birth to 4 healthy normal babies.