IVF Embryo Grading Explained: What It Means for Your Success Rates

Couples that try IVF often receive their embryo report grading embryos with 4AA, 3BB, or 5AB, and many embryos tell their patients that each letter and number combination can be confusing. In patients’ cases, these combinations can raise questions about embryo quality and chances of getting pregnant. 

 One method to determine embryo grading is to use developed and structural grading, and each of these grades is useful to identify which embryos have the greatest potential for implantation and being successful in helping with pregnancy.

The grades just mean that there is a journey when dealing with IVF and there is a process that is going to be completed. Knowing how to better analyze these grades can help one to become more positive, and in this blog, we will break down how embryo quality can determine success in IVF and how grading systems can influence how an embryo is determined.

What is Embryo Grading?

Embryo grading is a way to check the quality of embryos during IVF. In the lab, embryologists look at each embryo under a microscope and observe how it is growing. They do not touch or harm the embryo—this process is only for observation.

Embryos can look different from each other. Some may look more even and well-shaped, while others may look slightly uneven. However, even embryos that are not perfect in appearance can still grow normally and lead to a successful pregnancy.

IVF Embryo Grading Chart: Understanding Embryo Quality

For IVF, embryos grow in labs, during which specialist embryos check the formation and development of embryos by looking through microscopes. 

The majority of fertility clinics grade embryos using the Gardner Blastocyst Grading System. This calculates embryos’ grades using three criteria:

  • Stage of blastocyst expansion
  • Quality of the inner cell mass
  • Quality of the trophoblast

The combination of these three grades creates grades for embryos like 5AB, 4AA, and 3BB.

IVF Embryo Grading Chart (Lab-Style Table)

Grading Component

Grade

Description

Role in Pregnancy

Blastocyst Expansion

1

Early blastocyst forming cavity

Early embryo development
 

2

Blastocyst cavity forming

Continued development
 

3

Full blastocyst

Ready for further expansion
 

4

Expanded blastocyst

Higher implantation potential
 

5

Hatching blastocyst

Preparing to implant
 

6

Hatched blastocyst

Ready for implantation

Inner Cell Mass (ICM)

A

Many tightly packed cells

Develops into the fetus
 

B

Several loosely packed cells

Moderate fetal development potential
 

C

A few irregular cells

Lower developmental potential

Trophectoderm (TE)

A

Many healthy cells forming outer layer

Develops into the placenta
 

B

Moderate number of cells

Adequate placental support
 

C

Few uneven cells

Lower implantation support

Embryologists use this grading system to determine which embryos are most suitable for transfer or freezing during IVF treatment.

How to Read an Embryo Grade

Embryo grades consist of one number and two letters.

For example: 4AA

Component

Meaning

4

Expanded blastocyst

A

Excellent inner cell mass

A

Excellent trophectoderm

This indicates that the embryo is well developed with strong fetal and placental cell quality.

4AA vs 3BB Embryo: Key Differences

Many IVF patients want to understand the difference between embryo grades such as 4AA and 3BB, since these grades may appear in their IVF report.

Embryo Comparison Table

Feature

4AA Embryo

3BB Embryo

Blastocyst Expansion

Expanded blastocyst

Full blastocyst

Inner Cell Mass

Grade A – excellent

Grade B – moderate

Trophectoderm

Grade A – strong placental cells

Grade B – moderate placental cells

Overall Quality

Excellent

Good

Implantation Potential

Higher

Moderate

Although 4AA embryos are considered top quality, embryos graded 3BB can still lead to successful pregnancies and are commonly transferred in IVF cycles.

Embryo Quality Categories in IVF

To help patients understand embryo grades more easily, fertility specialists often group them into quality categories.

Embryo Quality

Example Grades

Interpretation

Excellent

4AA, 5AA, 6AA

Highest embryo quality with the strongest implantation potential

Best / Very Good

4AB, 5AB, 4BA

Very strong embryo quality with high chances of implantation

Good

3AA, 3AB, 4BB, 5BB

Good embryo development with favorable implantation potential

Average / Fair

3BB, 3BC, 4BC, 2BB

Moderate implantation potential

Poor

2BC, 3CB, 4CB

Lower embryo quality and reduced implantation chances

Discard / Very Low Quality

1CC, 2CC, 3CC, 4CC

Very low developmental potential and rarely used for transfer

It is important to remember that embryo grading does not guarantee pregnancy, and even embryos with moderate grades may result in healthy pregnancies.

What Embryo Grading Cannot Predict

Embryo grading is a helpful tool, but it cannot determine every aspect of IVF success.

Limitation

Explanation

Genetic health

Requires genetic testing (PGT)

Implantation certainty

Even top-graded embryos may not implant

Pregnancy outcome

Influenced by uterine health and maternal factors

Baby’s health

Embryo grade does not determine long-term health

For this reason, fertility specialists consider multiple factors when planning IVF treatment.

Why Embryo Grading Matters in IVF

Embryo grading helps doctors make important decisions during the IVF process.

Purpose

Benefit

Selecting embryos for transfer

Improves implantation chances

Choosing embryos for freezing

Preserves embryos with good potential

Planning IVF strategy

Helps determine transfer timing

Estimating success probability

Provides insights into embryo development

 

Conclusion

Evaluating embryo quality and determining which embryo(s) to transfer is done through embryo grading. The system analyzes and scores inner cell mass and trophectoderm quality and blastocyst stage development. Scores and grades are classified as 4AA, 3BB, and 5AB.

Grading embryos is based on potential; however, grading embryos is not an assurance of pregnancy. Age of mother, health of uterus, embryo genetics, and other aspects of fertility will determine the success of IVF. Knowledge of embryo grading can help couples gain confidence during the process.

With more than 60,000+ IVF cycles performed and success in over 12 countries, SCI IVF Hospital is considered the top and best IVF center in India. SCI IVF Hospital has advanced and improved the process of creating personalized IVF treatment plans, which evaluate embryos to maximize the potential of the couple(s) to become parents.