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Understanding Embryo Grading and How Success Correlates with Each Grade

09 Feb 2022

When it comes to embryos, we often receive questions about how we know if an embryo is a good candidate for transfer. After all, embryonic development is complex. This article is geared to help you get up to speed on the initial process of embryo incubation for the first seven days, how we grade our embryos at PFCLA, and what the differences are in grading and success rates.

What is embryo grading?

During the IVF process, embryos created in the lab are graded by the embryologists to determine which embryos have the best appearance under microscope.  Embryo grading enables embryologists to distinguish between good, average, and poor embryos in order to help the physician choose the embryo to transfer which has the highest chance of having a healthy baby. 

If you are going through IVF, you may have received an embryo report outlining the “grades” of your embryo(s). These can be difficult to understand, so we’ve written this guide to walk you through how embryologists come up with this grade and what it means for your chances of success.  

Embryo grading is a tool that your fertility specialists will use to determine 

  1. Which embryos to transfer
  2. How many to transfer
  3. And on what day of embryonic development.  

The day after the egg retrieval procedure, intended parents will learn how many embryos have been fertilized. In the following week, the fertilized embryos will be under culture for five to seven days and the embryologists will check on the embryos to see how they’ve progressed throughout that time. 

If you’ve selected to have PGT testing performed on your embryos, this is also when the biopsies will occur. 

An inside look at the embryo grading process

Every embryologist and IVF lab may vary in how they grade their embryos. Here is an explanation of how we grade embryos in our IVF Laboratory at PFCLA:  

Embryos are evaluated morphologically under a high-power microscope and graded based on certain visual criteria determined by experienced embryologists.

Embryos continue growing in the incubator from the moment they are created. A competent embryo must reach a certain stage of growth based on the number of cells it contains. The day after fertilization, an embryo is made of two cells. Over the next few days, these cells continue to divide to the point that on the 5th day after fertilization, they have created a “sheet” or a blanket of cells. Such an embryo is called a “Blastocyst”. Based on this growth and continued cellular multiplication, blastocysts are ranked as follows:

  • Early Blastocyst
  • Full Blastocyst
  • Expanded Blastocyst

The rate of success increases based on two factors:

  • Use of a genetically normal embryo
  • The morphological grading of an embryo

We culture embryos until day 7. Our in-house pregnancy rates have shown the following embryos to have the highest chance of success: these embryos yield similar success rates whether they are Day 5 or Day 6 embryos. The success rate depends on many other variables including the age of the egg source (regardless of how good an embryo is, age is often a critical factor in success rates for embryos). When the egg has been retrieved from a woman under 30 years old, we expect around a 70-75% success.

    • Expanded Blastocyst Grades I&II
  • Full Blastocysts Grades I

Embryos graded as a Blastocyst II have a slightly lower success rate but they are still considered good embryos even if they are Day 5 or Day 6 embryos.

Embryos of Grade III or Day 7 embryos have the lowest success rates of <20%.

As mentioned earlier, the success rate also depends on the age of the woman who is using her eggs. The references below are based on embryos created by egg donors under the age of 30. 

  • Day 5 Expanded Blastocyst Grade I or Hatching Expanded Blastocyst Grade I 70%
  • Day 5 Expanded Blastocyst Grade II 70%
  • Day 5 Blastocyst Grade I 70%
  • Day 6 Expanded Blastocyst Grade I or Hatching Expanded Blastocyst Grade I 70%
  • Day 6 Expanded Blastocyst Grade II 50%
  • Day 5 Blastocyst Grade II 50%
  • Day 5 Early Blastocyst Grade I 40%
  • Day 6 Blastocyst Grade I 40%
  • Day 6 Blastocyst Grade II 30%
  • Day 5 Blastocyst Grade III or Early Blastocyst Grade II <20%
  • Day 5 Any Grade III embryo <10%
  • Day 6 Any Grade III embryo <10%


Bring your family to life with the advanced embryo grading processes of PFCLA

At PFCLA, our goal is to give our patients the highest chance of having a successful pregnancy and a healthy baby. It is helpful to learn more about Preimplantation Genetic Testing  and Single Embryo Transfers. If you would like to book a consultation to speak to one of our specialists, please click here

Note: This is not intended to be a substitute for professional medical advice, diagnosis or treatment. Information provided is for general educational purposes only and is subject to change without notice. Speak to your doctor directly with any questions you may have regarding a medical condition. Any information contained herein does not replace any care plan as determined by a physician. 

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