This is an oocyte-cumulus complex which is identified in the follicular fluid (aspirated during egg collection) when this is scanned under the stereozoom microscope in the IVF lab. Note how shapeless the egg is, and how difficult it is to judge egg quality by just looking at it under the microscope.
This is what a mature oocyte looks like when the surrounding cumulus cells have been stripped off, prior to doing ICSI. Note the small polar body at 6 o'clock which shows that this a mature egg - in metaphase II.
On a casual inspection, this looks like a good 2-cell embryo, since there are no fragments, and the cells are equal. However, the lower cell has 2 nuclei. Embryos which have multi-nucleate blastomeres have a lower chance of implanting, and should not be transferred. I chose this image to emphasise how important the skill and experience of the embryologist is !
This is a 3-cell embryo on Day 2 with fragmentation. Though the blastomeres are equal, about 20% of the embryos is occupied by small bubble like structures called fragments. This makes it a Grade B embryo. These fragments arise as a result of cell death, called apoptosis. Though this embryo has a lower chance of implanting as compared to a Grade A embryo, many of them do implant successfully, and the babies which result from these are completely normal.
These are 4 embryos on Day 2 from one patient. This picture emphasises how much variability there can be in embryo development, and we still don't know why some embryos do so well, while others do so poorly. The skill of the embryologist lies in selecting the best embryo(s) for transfer.
This image shows that on Day 2, one embryo has only 2-cells, while the other one has 4-cells. The 4-cells embryo has a better chance of implanting because it is dividing more rapidly.
2 blastocysts on Day 5. If you had to select only one to transfer, the one on the left is a better choice, because it is larger (and has expanded more).