The importance of the trophectoderm
The trophectoderm is the outermost layer of cells in the blastocyst which makes contact with the endometrium and establishes the embryo's means of receiving nutrition. The trophectoderm gives rise to the placental cells and therefore plays a crucial role in the embryo's development through pregnancy.
Several papers have highlighted the impact of high and low grade trophectoderm on the rate of pregnancies; it has been consistently demonstrated that a higher quality trophectoderm is linked with higher implantation and live birth rate.
While, the primary focus on embryology grading used to be on the inner cell mass, grading the trophectoderm is starting to rise in import.
Our lab has a cutoff grade for tropectoderm (and ICM) and we have routinely seen poor grade trophectoderm embryos to give us poor thaw survival, low euploid rates, poor DNA quality in biopsies, and a lower overall pregnancy rate. Because of this we try to be more thorough in grading our trophectoderm.
The above embryo has a lot of trophectoderm! By our estimate, there are well over 100 cells here. It's hard to believe this was just 8 cells around 48 hrs ago!