Embryo quality and grading – does it affect success?

The quality and grading of embryos has a big impact on the success of assisted reproductive technologies like in vitro fertilisation (IVF). When you undergo IVF, the goal is to choose the best-quality embryos to increase your chances of a successful pregnancy. But what exactly is embryo quality, how do we determine it, and does it really affect the outcome? Let’s dive deeper into this topic to gain a better understanding.

What is embryo quality?

After fertilisation, the fertilised eggs are called embryos. Embryo quality refers to the stage of development and appearance of these embryos. Around 12 hours after fertilisation, the embryos start dividing, and this growth continues for up to six days. Our skilled and experienced embryologists carefully assess the embryos at various stages during this growth period for grading purposes. It’s an important process that requires both time and expertise.

The evaluation of the embryos is crucial as it allows us to choose the embryos that will either be transferred into the uterus or frozen for future use. Our embryologists observe your embryos from beginning to end, taking care of them day by day, in order to select the best candidate for your future baby. Nobody understands embryo quality better than our embryologists, and they can help you to understand the quality of your embryo.

Cleavage stage embryos and blastocysts

By day two and three after egg collection, the embryos are called cleavage stage embryos. They are graded based on the evenness of their cells and the presence of any fragmentation. The more evenly the cells divide and the less fragmentation, the higher the grade and better the embryo quality. Day three embryos have between six and eight cells.
Although we don’t count cells on day five, the embryos will have between 64-128 cells and are called blastocysts. Blastocysts are made up of an inner cell mass (ICM) and an outer layer called the trophectoderm. The ICM cells develop into the baby, while the trophectoderm cells form the placenta.

Embryo grading

Embryo grading is a helpful way to choose the best embryos for transfer to increase the chances of a successful pregnancy. We examine both the ICM and trophectoderm cells when grading blastocysts. High-grade embryos have a large ICM and a well-formed trophectoderm layer, making them a promising choice for successful implantation and healthy growth. But it’s important to remember that embryo grading isn’t a guarantee of success and lower-grade embryos can still lead to a successful pregnancy.

Transferring embryos

When it comes to transferring embryos, blastocyst transfers, where embryos have had more time to develop in the lab, generally have higher success rates compared to cleavage stage transfers. However, not all embryos reach the blastocyst stage, and some may not survive until this point. In those cases, transferring embryos at the earlier cleavage stage could have led to successful pregnancies.

Factors like a woman’s age, the number of embryos available and the quality of the eggs can influence whether a blastocyst transfer is recommended. Younger women with a good number of embryos are usually more likely to undergo blastocyst transfers. Older women, those producing fewer healthy eggs, or couples with limited embryo availability may opt for cleavage stage transfers to ensure viable embryos for transfer.


It is important to remember that embryo quality and grading are just one piece of the puzzle. Success in IVF depends on several factors, including a woman’s reproductive health, uterine environment and the overall treatment plan from fertility specialists. Each person’s situation is unique, and the guidance of our fertility professionals at Leicester Fertility Centre can help you make informed decisions.