Understanding Embryo Grading Scales

Understanding embryo grading scales can help you make informed decisions during IVF.

Embryo grading scales are used by fertility clinics to evaluate the quality of embryos created through in vitro fertilization (IVF). These grades can help your fertility specialist determine which embryos will be ideal for the embryo transfer.

Fertility clinics can help you create embryos and determine embryo grades. Contact us to find a fertility clinic near you.

In this article, we’ll break down the different embryo grading scales for both Day 3 embryos and Day 5 blastocysts, and explain how grading impacts outcomes.

Understanding Embryo Grading Systems

Embryo grading can vary between fertility clinics, with some using different grading systems or scales. One commonly used system is the Gardner grading scale, which is specifically designed for evaluating blastocysts. The SART Grading Scale is another common grading scale for assessing embryos.

While the exact embryo grading scale may vary somewhat from clinic to clinic depending on the grading system used, generally it is important to know whether the grading scale and embryo is for a day 3 embryo or a day 5 embryo, as the structure of the embryo can change significantly between these days of development.

Day 3 Embryo Grading: Good, Fair, Poor

On day 3, embryos are evaluated primarily on the following parameters:

• Cell Number: The ideal number of cells is typically between 6 and 10.
• Symmetry: Symmetrical embryos are preferred.
• Fragmentation: Lower fragmentation rates indicate better quality.

Day 3 Grading Scale

The day 3 grading scale usually ranges from 1-4 or A-D, depending on the clinic:

• Grade 1/A: Optimal quality low fragmentation, symmetrical.
• Grade 2/B: Fair quality some fragmentation, mostly symmetrical.
• Grade 3/C: Poor quality high fragmentation, asymmetrical.
• Grade 4/D: Non-viable high fragmentation.

Day 5 Blastocyst Embryo Grading: Good, Fair, Poor

By day 5, embryos develop into blastocysts and are evaluated using a three-part grading system:

Day 5 Grading Scale

Expansion Scale (1-6):

Inner Cell Mass Quality:

Trophectoderm Quality:

Understanding Common IVF Embryo Grading Systems

Embryo grading scales often combine grading factors to give an embryo an overall grade.

Interpreting Day 3 Embryo Grades

For day 3 embryos, depending on the scale, an embryo may receive a 1-4 or an A-D grade that is based on multiple factors, including the number of cells and the fragmentation of the cells.

Generally, an embryo with a grade of 1 or A is more likely to become a pregnancy than an embryo with a grade of 2 or B or 3 or C.  

Interpreting Day 5 Embryo Grades

On day 5, embryos may receive a 6AA as the highest score, down to a CC1 as the lowest score.

Here are some examples of grades an embryo may receive and possible reasons for the grading:

• 4AA Embryo Grading: A high-quality embryo with excellent ICM and TE development, ideal for transfer.
• 5AB Embryo Grading: A good-quality blastocyst; slightly less developed than a 4AA but still a viable option for transfer.
• 4BB Embryo Grading: A fair-quality embryo; still usable but may have a lower likelihood of successful implantation.
• 3AA Embryo Grading: A good-quality day 5 embryo, indicating optimal cell count and symmetry.
• 5BB Embryo Grading: A moderate-quality blastocyst, which may have a reasonable chance of success but is less favorable than higher grades.

How Grading Affects Transfer Decisions

Embryo grading plays a significant role in deciding which embryos to transfer. Higher-grade embryos (like 4AA or 5AA) are typically preferred for transfer due to their increased chances of successful implantation.

Lower-grade embryos (like 3BB or 4BB) may still be transferred, but the likelihood of success is generally lower.

If you have low-graded embryos, surrogacy may increase your chances of successful pregnancy as compared to traditional IVF. Contact a surrogacy professional now or learn more here.

Factors Beyond Grading That Influence Outcomes

While embryo grading is important, it is not the sole determinant of success. Several other factors also play a crucial role:

• Maternal Age: Generally, younger mothers tend to have higher success rates with embryo transfers.
• Uterine Environment: The health and receptivity of the uterus can significantly affect implantation.
• Overall Health: The mother’s health and lifestyle factors can influence pregnancy outcomes.

If you have embryos ready, you can be matched with a surrogate in an average of 1 - 6 months. Learn more about available surrogates or get connected to a surrogacy professional now.

Frequently Asked Questions

Is 4AA or 5AA better?

A 5AA embryo is typically considered better than a 4AA due to its more advanced stage of development and overall quality.

What is a good embryo grading?

A good embryo grading usually includes grades A or B, which indicate optimal development and a higher chance of successful implantation.

Is a 4BB embryo good?

A 4BB embryo is considered fair quality. While it may have a reasonable chance of success, it is not as favorable as higher-grade embryos.

What grade is good for embryo transfer?

Grades A and B (such as 4AA, 5AA, or 5AB) are generally considered good for embryo transfer, as they indicate a higher likelihood of successful implantation.