Embryo Grading Explained: What Those Numbers Mean for Your IVF Cycle

Many factors affect the success of in vitro fertilization (IVF), including the health of the embryo. Fertility doctors use a grading system to evaluate the quality of each embryo. 

You may receive an embryo report that includes these grades and wonder what it all means. The team at CARE Fertility in Bedford and Fort Worth, Texas, is here to help you have a better understanding of embryo grading so you can feel informed and confident in your IVF journey.

What is embryo grading?

An embryo is an early developmental stage — from fertilization through about eight weeks. Embryo grading is a system lab specialists use to assess the visual quality of an embryo.

In the lab, specialists look at embryos at around day four or five and grade them based on the qualities they see. The grading system evaluates the appearance of the embryo, not the genetics. 

Fertility specialists use the tool to determine which embryos are best suited for implantation. The grading takes into consideration the size and cell mass of the embryo and the cell mass of the trophectoderm, the cells that form into the placenta.

Understanding the number

The number is the first marker of the grading tool, and it determines the size of the embryo, also called a blastocyte. The grading system ranges from 1 to 6 and indicates:

• 1-2: Early blastocyte
• 3: A full blastocyte
• 4: An expanded blastocyte
• 5: Hatching blastocyte
• 6: Fully hatched blastocyte

The number shows the developmental stage of the blastocyst — how much it has grown and whether it has broken out of its shell.

What the first letter means

The first letter of the embryo grade indicates the inner cell mass, or the cells that eventually form into the fetus. Only embryos  with a number grade between 3 and 6 receive a first letter grade.

• A: Many tightly packed cells
• B: Moderate amount of healthy cells
• C: Fewer healthy cells

Embryos with more healthy cells may mean there’s a greater chance of having a successful pregnancy. 

What the second letter means

The second letter of the embryo grade relates to the trophectoderm, which are the outermost layer of cells that form into the placenta. This part of embryo grading is similar to the first letter:

• A: Numerous cells
• B: Moderate amount of cells
• C: Few cells or irregular cells

Like the inner cell mass, the greater number of healthy trophectoderm cells may mean a greater chance of success.

What your embryo grade means

Your fertility doctor reviews the details of the embryo grades with you and provides context. In general, the embryo grade is a visual evaluation of the size and health of the cells that will form into the fetus and placenta. 

A grade of 4AA means you have an expanded blastocyte with a robust and healthy inner cell mass and trophectoderm. A grade of 5AB means the blastocyte is hatching and has excellent inner cell mass and good trophectoderm.

While embryo grading can help find healthy embryos for IVF, it’s not a cut and dried process that can predict final outcomes. Other factors can affect the success of your IVF, such as chromosomal health, maternal age, and health of the uterus.

When it comes to selecting embryos for implantation, the CARE Fertility team uses a combination of factors to make decisions, including embryo quality, genetic information, and your personal health history.

As you undergo IVF, our team can provide the guidance, testing, and support you need to help make informed decisions. Call us today at 817-540-1157 or send a message online to schedule a consultation.