|Grading human preimplantation embryos. Courtesy : nature.com|
Your embryos are graded according to their microscopic appearance and are given a rank (like grade A, grade B, grade C and so on). A day 3 embryo which gets the topmost grade will have 8 cells which are equal in size, with all cells having single nucleus , without any fragments. If you have 10 embryos, not all of them will be of top grade on day 3. Some will have a fewer number of cells, some might have uneven cells, while others may have lots of fragments. The doctor will select the best embryos from amongst these (the top grade embryos) , and transfer these to the uterus . The remaining embryos can be frozen, if they are of good quality. But what happens if all your embryos are of poor quality? Why does this happen ? There are 2 possibilities :
- The embryology lab had some technical problems, and failed to create good embryos
- The quality of your egg is not good , which is why the cells did not divide properly, and hence the embryos appear poor morphologically
To rule out the first possibility , insist that your embryologist show you photos of the embryos of other patients who were treated on the same day . If these are good quality, this means the chances of their being a lab problem are small.
If this has been ruled out, then remember that the commonest reason for poor quality embryos is poor quality eggs. It’s the mitochondria in the cytoplasm of the egg which provide the energy for cell division. If the eggs are of poor quality , their mitochondria cannot provide enough power to drive normal cell cleavage, which is why the embryo may arrest; or the cells may have lots of fragments. Unfortunately, there is no method to test egg mitochondrial quality as yet.
However, do remember that grading is a very crude tool and that the appearance of your embryo cannot predict its ability to give rise to a baby accurately. Poor grade embryos do give rise to a healthy baby , while many good looking embryos fail to do so !