Factors that can influence whether an embryo will carry to term are very diverse. From endometrial receptivity, poor quality eggs and sperm and even infections leading to diseases such as chronic endometritis without the patient’s knowledge. In addition, one of the most important factors is the quality of the embryos.
It is important that they develop correctly, but even more important that they are free of chromosomal abnormalities.
Nowadays, in IVF treatments there are techniques to analyze and classify the embryos before transferring them to the patient, in order to increase her chances of pregnancy.
For IVF treatments we work with day 3 embryos or with blastocysts (days 5-6). Depending on whether we act with one or the other, the classification is different.
Classification of day 3 embryos
The day 3 embryos are classified into 5 grades: 1, 2, 3, 4, and 5, with those in group 1 having the highest quality.
The morphology of each embryo wasdetermined by Lucinda L. Veeck*:
- Grade 1: blastomeres of equal size and no cytoplasmic fragments.
- Grade 2: blastomeres of equal size with minor cytoplasmic fragments or blebs.
- Grade 3: blastomeres of distinctly unequal size with few to no cytoplasmic fragments.
- Grade 4: blastomeres of equal or unequal size with significant cytoplasmic fragmentation.
- Grade 5: few blastomeres of any size and severe or complete fragmentation.
Classification of the blastocyst
For their part, blastocysts are classified with 2 letters, one for ICM (Inner Cell Mass) and one for trophectoderm cells. In addition, the Gardner system can also be used, which in addition to the letters provides a degree of expansion (from 1 to 5). So based on this classification, a blastocyst could be, for example, 4AB.
To classify the blastocysts, other parameters different from those of day 3 embryos are taken into account, which are:
1. Size, shape and compaction of the structure of the ICM.
2. Structure and number of cells of the trophectoderm.
3. Degree of expansion.
4. Adequate evolution during development until reaching the blastocyst stage.
The success of an IVF: how it affects embryo quality
After all that has been seen above, we come to the conclusion that the higher the embryo quality, the more likely it is that the implantation in the uterus of the day 3 embryo or the blastocyst will take place.
In any case, it must be considered that there are also other factors that may determine the knowledge of the implantation window and the conditions of the endometrium.
* Veeck L: An Atlas of Human Gametes and Conceptuses. AnIllustrated Reference for Assisted Reproductive Technology, 1999.