Embryo Quality: How Is It Assessed and What Influences the Chance of Implantation? 

Embryo quality is assessed during cultivation – most commonly on day 3 and day 5 after fertilization. The embryologist observes how quickly and evenly the embryo divides, how many cells it has, their shape, and whether there are signs of damage. On day 5, they evaluate whether the embryo has reached the blastocyst stage and how well its individual structures have developed.

The result is an assessment that helps determine which embryo has the highest chance of successful implantation. This depends on a combination of three factors: the genetic health of the embryo, the readiness of the uterine lining, and the quality of the laboratory environment.

How Does an Embryologist Assess Embryo Quality?

The evaluation process is not a single moment but a several‑day observation that begins immediately after fertilization.

Day 3 After Fertilization: Number of Cells and Their Condition

At this stage, the embryo ideally has 6 – 8 cells. The embryologist evaluates:

• Number of cells – the correct number for the day of cultivation indicates healthy development.
• Symmetry – cells should be roughly equal in size and regularly arranged.
• Fragmentation – small cytoplasmic fragments formed during division; a certain degree is normal, but fragmentation above 25% reduces the likelihood of further development.

Day 5 After Fertilization: Blastocyst and Its Assessment

Embryos that develop properly reach the blastocyst stage around day 5. At this point, the embryologist distinguishes three structures:

• Blastocoel – a fluid‑filled cavity; its expansion indicates ongoing development.
• Inner cell mass (ICM) – the group of cells that will develop into the fetus.
• Trophectoderm (TE) – the outer cell layer that will form the placenta.

Assessment on day 5 has the greatest predictive value regarding embryo quality.

At Prague Fertility Centre, we also use time‑lapse monitoring – a special incubator with a camera that records embryo development every few minutes. This provides a complete developmental record without removing embryos from optimal conditions or exposing them to unnecessary stress.

How Embryo Quality Is Expressed: The Gardner Scale

Once the embryo reaches the blastocyst stage, it is time for a specific evaluation. Most embryology laboratories worldwide – including ours – use the Gardner scale.

Each embryo receives a three‑part score:

• a number from 1 – 6 indicating blastocoel expansion; higher numbers mean more advanced development; grades 5 and 6 indicate that the embryo is beginning or has completed ​“hatching” from the zona pellucida,
• a letter A – C assessing the inner cell mass; A indicates compact, well‑defined cells with high developmental potential,
• a second letter A – C evaluating the trophectoderm; A again indicates a regular, dense cell layer suggesting a strong placenta.

The final score may look like 4AA or 3BC. Embryos rated 4AA or 5AA are among the most promising.

However, this assessment is not a final verdict. Even embryos graded BB or BC have resulted in healthy pregnancies. Morphology is only one perspective. Embryo development is dynamic, and its chances are not defined by a single number or letter. The expertise and experience of the embryologist also play a crucial role.

What Can You Do to Improve Embryo Quality?

While genetics are fixed, the condition of reproductive cells can be influenced. 3 – 4 months before treatment:

• Limit or stop alcohol and smoking – both demonstrably worsen embryo quality from both egg and sperm perspectives.
• Maintain moderate physical activity and healthy sleep.
• For men: avoid overheating the testicular area (saunas, hot baths, tight underwear), as sperm are heat‑sensitive.
• Consult your doctor about dietary supplements – vitamin D, folic acid, coenzyme Q10, or omega‑3 fatty acids usually support reproductive cell health.
• Mental well‑being: stress may not directly affect the embryo, but it influences hormonal balance and uterine blood flow, which are key for implantation.

What Is the Chance of Embryo Implantation and What Does It Depend On?

Embryo quality is crucial when deciding on a transfer, but it is not the only variable. Implantation depends on a promising embryo and a receptive uterine lining.

Endometrial readiness is monitored by ultrasound, and in cases of repeated unsuccessful transfers, our physicians may use advanced diagnostics such as ERA or beReady tests. These precisely determine the implantation window – the optimal timing for transfer.

We also offer supportive methods:

• LAZT – laser‑assisted hatching that thins the embryo’s protective обол, facilitating ​“hatching,” which is necessary for contact with the uterine lining.
• EmbryoGlue – a special medium mimicking the uterine environment that helps the embryo adhere; according to available data, it can increase implantation success by up to 19%.

Interestingly, frozen embryos often have comparable – sometimes even higher – implantation rates than fresh ones. After stimulation, the woman’s body may be hormonally burdened, and the lining may not be optimal. In such cases, we often recommend cryotransfer in a subsequent cycle.

What Does Low Embryo Quality Mean and What Are the Other Options?

As mentioned earlier, poorer embryo grading does not mean treatment failure or lack of options.

The first step is often extended cultivation. Some embryos that look less promising on day 3 can catch up by day 5 or 6 and reach a well‑rated blastocyst.

If a good‑quality embryo exists but there are genetic concerns (e.g., higher maternal age or previous failures), we offer preimplantation genetic testing, allowing us to check for chromosomal abnormalities before transfer.

For couples who repeatedly produce low‑quality embryos, a combined IVF cycle may help – fertilizing both the woman’s own eggs and donor eggs. We compare embryo development from both groups and select the most promising embryo for transfer, regardless of origin. This approach also provides valuable insight into whether egg quality is the underlying issue.

Each patient is cared for from start to finish by one physician, who evaluates cultivation results in the context of the full medical history. Before transfer, the embryologist personally explains embryo development and answers all questions.

If you would like to explore your options, come for a free consultation. Together, we will review your situation and propose the most appropriate approach for you.

How Embryo Quality Is Assessed: The Gardner Scale

Once an embryo reaches the blastocyst stage, it is time for a more specific evaluation. Most embryology laboratories worldwide – including ours – use the Gardner grading system.

Each embryo receives a three-part score:

• a number from 1 – 6 indicating the degree of blastocoel expansion; the higher the number, the more developed the embryo is. Grades 5 and 6 mean that the embryo has begun or has already completed ​“hatching” from its protective shell (zona pellucida),
• a letter from A – C assessing the inner cell mass; A indicates compact, well-defined cells with a high potential for fetal development,
• a second letter from A – C evaluating the trophectoderm; A again represents a regular, dense layer of cells suggesting strong placental potential.

The final score may look, for example, like 4AA or 3BC. Embryos graded 4AA or 5AA are considered among the most promising.

However, grading is not a final verdict. Even embryos graded BB or BC have resulted in healthy pregnancies. Morphology is only one perspective from which embryo quality is assessed. Embryonic development is not static, and its potential cannot be defined by a single number or letter. The expertise and experience of the embryologist performing the assessment also play a crucial role.

What Can You Do to Improve Embryo Quality?

Genetic makeup cannot be changed, but the condition of reproductive cells can be influenced. Three to four months before treatment, we recommend:

• Reducing or eliminating alcohol and smoking – both are proven to negatively affect embryo quality from both the egg and sperm perspective,
• Paying attention to moderate physical activity and quality sleep,
• For men – avoiding overheating of the testes (sauna, hot baths, tight underwear), as sperm cells are sensitive to heat,
• Consulting supplements with your doctor – vitamin D, folic acid, coenzyme Q10 and omega‑3 fatty acids generally support the condition of reproductive cells,
• Psychological well-being: while stress does not directly affect the embryo, it impacts hormonal balance and uterine blood flow, both of which are essential for successful implantation.

What Is the Chance of Embryo Implantation and What Does It Depend On?

Embryo quality is crucial when deciding on transfer, but it is not the only factor. Implantation depends on both a viable embryo and a properly prepared uterine lining.

Endometrial readiness is monitored by ultrasound. In cases of repeated failed transfers, our physicians may use advanced diagnostics such as ERA or beReady endometrial receptivity tests, which precisely determine the so‑called implantation window – the optimal timing for embryo transfer.

To support implantation, we also offer additional methods:

• LAZT – laser‑assisted hatching, which thins the embryo’s protective shell and facilitates its ​“hatching”, a prerequisite for contact with the uterine lining,
• EmbryoGlue – a special transfer medium that mimics the uterine environment and helps the embryo adhere to the endometrium; according to available data, it can increase implantation success rates by up to 19 %.

Interestingly, frozen embryos often show comparable – and sometimes even higher – implantation rates than fresh transfers. After egg retrieval, a woman’s body is hormonally burdened, and the endometrium may not be in an ideal condition. For this reason, we sometimes recommend cryotransfer in a subsequent cycle.

What Does Low Embryo Quality Mean and What Are the Next Options?

As already mentioned, a poorer embryo grade does not mean that treatment has failed or that no further options exist.

The first step is often extended culture. Some embryos that appear less promising on day 3 may catch up developmentally by day 5 or 6 and reach the blastocyst stage with good grading.

If we have an embryo with good morphological quality but concerns remain regarding genetic integrity (for example due to higher maternal age or previous failures), we offer preimplantation genetic testing (PGT). This allows us to verify, prior to transfer, whether the embryo has chromosomal abnormalities.

For couples who repeatedly produce embryos of low quality, a combined IVF cycle may be helpful. In this approach, both the patient’s own eggs and selected donor eggs are fertilised. We compare the development of both embryo groups and select the most promising embryo for transfer, regardless of origin. This approach also provides valuable information as to whether the issue lies primarily in the eggs.

If you would like to explore your options, we invite you to a free consultation. Together, we will review your situation and propose an approach that makes the most sense specifically for you.