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Gardner Grading System

What is it?

Have you heard of this term and not really understood what it meant? Had it mistaken for a “gardener”? Don’t worry, you’re not the only one. The Gardner grading system is a grading system for blastocysts based on their morphology (the shape, size, and appearance). The system was created by D. K. Gardner and W. B. Schoolcraft back in 1999. It is now used by many IVF laboratories as a tool to help measure blastocyst growth and the quality of the inner cell mass and trophectoderm. 

A collection of parameters are graded. One of these is the embryo cavity size, how far the embryo has come, hatching and emerging from the zona pellucida (membrane around the embryo). This is the numerical grades that goes from 1-6 unlike the grading system for the inner cell mass, and trophectoderm, which use alphabetical grades. 1 is used for the smallest blastocysts (and cavities, called blastocoel) and 6 is used for an embryo that has fully escaped its zona. 

The quantity and quality of individual cells is also graded using alphabetical designation (A-C), the inner cell mass and trophectoderm are each given a letter grade. Embryologists are looking for a lot of small, evenly sized cell that are clear and tightly linked together. The ICM should be a good size with a tight border, and the trophectoderm should resemble a quilt. 

Grading limitations

As useful as the Gardner and Schoolcraft system is, there are certain important areas that it does not cover according to “The Blastocyst,” by Thorir Hardarson, Gayle Jones, and Lisbet Van Landuyt. These areas certainly aid in selecting the best embryos for transplantation. These include the generation of cytoplasmic strings that can help keep cells together. Additionally, the perivitelline space and blastocyst cavity are two regions that are home to certain structures. 

Additionally, beautiful “perfect grade” blastocysts can easily be genetically abnormal. 

Final thoughts

Embryo grading systems such as the Gardner system play an essential role in deciding which embryo should be transferred into the womb first. We once again want to reiterate what is often said about embryo grading. While it is a great tool in deciding which embryos are likely to have the best fate in the womb, even the best guesses may sometimes not yield the expected results. In other words, a highly graded embryo may not do well in the womb while a poorly graded embryo actually does.

At the end of the day, they are tools to help embryologists to make the most well-informed decision that can. Embryologists train heavily for this purpose. The ART Compass app helps in optimizing lab performance and ensuring all embryologists are grading embryos similarly, from the most junior staff to the most senior. They are the most qualified people to perform the job and the embryos are always in good hands. 


Thorir Hardarson, Lisbet Van Landuyt, Gayle Jones, The blastocyst, Human Reproduction, Volume 27, Issue suppl_1, August 2012, Pages i72–i91, https://doi.org/10.1093/humrep/des230