Embryo fragmentation is a phenomenon that takes place in most embryos and its origin is not entirely clear. Some studies would seem to suggest that the fragments come from cell remains that have no nucleus or that they are the result of the decomposition of one or more cells from the embryo itself. The oocyte plays the most important role in fragmentation. Poor oocyte quality can lead to embryos that are highly fragmented. Embryo quality is determined by several characteristics such as the number of cells, their size or if the cell interior has an abnormality of any kind such as granularity or vacuolisation.
Types of embryo fragmentation
However, one of the factors that has most impact on embryo quality is the extent of fragmentation. Based on the amount, in percentage, of space that it occupies, fragmentation is categorised into 4 types or degrees.
- Grade 1: the fragments take up less than 10% of the free space between cells. FIGURE A.
- Grade 2: the fragments take up between 10 and 25%. FIGURE B.
- Grade 3: the fragments take up between 25 and 35%. FIGURE C.
- Grade 4: the fragments take up more than 35 % of the free space between cells. FIGURE D.
The fragments in an embryo can increase or decrease over the course of embryo development. It is less common for them to decrease. The main issue with fragmentation is that it impedes appropriate division of the cells that the embryo is made of. This can lead to slow development and, as a result, embryos that have a limited ability to implant in the mother’s uterus.
Some techniques such as fragment removal are used in order to eliminate fragments by means of aspiration. However, its use and its benefits are highly controversial because they involve a significant amount of embryo handling.
It is important to highlight the fact that numerous factors play a part in embryo implantation and the ensuing pregnancy. Therefore, an embryo with grade 1 fragmentation will not always implant and, likewise, an embryo with grade 4 fragmentation could lead to a pregnancy.