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| 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 !
