Patients often find themselves amazed when they first see photos of their embryos on the morning of their transfer. On this day, each embryo is meticulously examined under a powerful microscope, and patients receive important information about the quality of their embryos before the transfer takes place. Three main factors are evaluated: the number of pro-nuclei, the cell count, and the embryo grade. This information helps guide decisions about how many embryos to transfer, how many to freeze, and what to do with embryos that are not developing optimally.
Assessing embryo quality entails much more than what appears on the surface. Embryo evaluation is a standard practice in fertility clinics around the world, enabling embryologists to offer you and your healthcare provider essential insights into your embryos and overall fertility.
After eggs are retrieved from a patient’s ovaries, they are surrounded by numerous helper cells, making it difficult to assess their quality right away. For patients undergoing ICSI (Intra-Cytoplasmic Sperm Injection), these helper cells are removed, yet little information on quality can still be determined. Typically, only noticeably poor-quality eggs exhibit clear differences when compared to healthy ones. The majority of eggs do not display obvious quality indicators, so embryologists usually refrain from commenting on egg quality.
On average, about 70% of retrieved eggs will fertilize, regardless of quality. However, a high fertilization rate doesn’t necessarily predict better embryo quality.
Evaluation Process
The evaluation process begins with checking fertilized eggs for the presence of two pro-nuclei (PN) at their centers. Each pro-nucleus contains DNA from one parent, and in 95% of fertilized eggs, this aspect is standard. Occasionally, nuclear abnormalities may be detected, such as an uneven number of pro-nuclei or size irregularities. These abnormalities suggest that the embryos may not be viable, and patients will be informed accordingly.
All fertilized embryos are typically kept in the lab for a minimum of 48 hours before the transfer procedure. Only those with severe abnormalities—like those fertilized by multiple sperm—are discarded. Even eggs lacking visible signs of fertilization are preserved in case they fertilize later on. Observations are limited until the transfer time approaches, as the embryos need to remain undisturbed in the incubator.
During incubation, the fertilized egg begins to divide. This first cell division occurs within 12 hours post-fertilization, and afterward, the cells continue to split approximately every 16 hours. This ongoing process of division is crucial, as embryos have only 4 to 5 days to develop enough cells for implantation in the uterus. By the third day, an embryo is expected to have around 8 cells. Embryos with significantly fewer cells, such as 4 or fewer, face much lower chances of leading to a successful pregnancy. The cell count is a vital element in assessing embryo quality, and patients will be provided with this information.
Cell Appearance and Grading
Another factor in quality assessment is the appearance of the cells. Some embryos may exhibit uneven or asymmetrical cells, while others might have cells that are disintegrating. Cellular fragments from this disintegration are only quality indicators when they are severe. In fact, around 20% of embryos have no fragments at all, but the absence of fragmentation doesn’t guarantee pregnancy, as many other factors contribute to embryo quality.
The degree of fragmentation and cell symmetry is graded on a scale of 1 to 3. Grade 1 embryos appear healthy and normal. Grade 2 embryos may have slight fragmentation or unevenness but are still considered high quality. Only embryos that exhibit significant issues, such as having more fragments than whole cells, receive the unfortunate Grade 3 designation. These embryos are rarely capable of implantation and are not deemed suitable for freezing.
While cell number significantly predicts embryo quality, the grade primarily helps determine which embryos to transfer or freeze. The grade allows for ranking when multiple embryos share the same cell count, but its association with quality is only loose. Poorly graded embryos typically do not implant successfully, though other factors, like the patient’s age, play a far more critical role in predicting pregnancy rates. Interestingly, there’s no correlation between embryo grade and genetic health; genetically abnormal embryos can be graded as well as genetically normal ones. Furthermore, pregnancies resulting from Grade 3 embryos do not carry a higher risk of birth defects than those from Grade 1 embryos.
Additional Resources
If you’re interested in learning more about pregnancy and home insemination, check out this excellent resource on artificial insemination. And for those on the journey to parenthood, explore our 2023 Holiday Gift Guide for thoughtful ideas. Don’t forget to visit Make a Mom for their innovative at-home insemination kits.
Conclusion
In summary, evaluating embryos involves a detailed assessment of various factors, including pro-nuclei presence, cell count, and grading of cellular integrity. While these elements provide insight into embryo viability, factors like the patient’s age and genetic background have a more significant impact on the likelihood of a successful pregnancy.