Why are all embryos not top quality embryos?
The purpose of examining the oocytes and embryos carefully and taking pictures of them every day is to find the embryo that develops into specific stages at a given time. By following each embryo carefully, you can identify which one has the greatest opportunity to result in a normal pregnancy. In the following we will give a few examples of embryos that are not top quality or not suitable for transfer back into the uterus.
No 1: Oocyte not properly fertilised
It has only a single pronucleus, and thus presumably only 23 chromosomes instead of 46. Such oocytes may well begin to cleave, although their content of chromosomes is not correct. But they give no pregnancies, and hence are not transferred into the womb.
No. 2: 3 pronuclei
The oocyte has 3 nuclei. This means that it contains 69 chromosomes instead of 46 chromosomes. It will not give rise to a healthy child. Three pronuclei are observed when the oocyte has been fertilised by 2 sperm cells (this is due to an error in the oocyte that allows 2 sperm to penetrate). It may also be due to a maturation defect in the oocyte, resulting in a double set of chromosomes of what it must have at the time of fertilisation.
No. 3: Immature oocyte
Some oocytes can not fertilise. The reason is usually that they are immature. Oocytes from small follicles are more likely to be immature.
No. 4: Dead cell
The oocyte has perished and has therefore become atretic. Although it resembles an oocyte, the cell is dead and unable to be fertilised or cleave.
No. 5: Single polar body
Oocyte no. 5 has two pronuclei, however, it contains only one polar body (arrow). The shape of the oocyte is also wrong. This means that the oocyte is not healthy. Although the oocyte can start cleaving, it will not develop into a healthy child.
No. 6: Inappropriate cell division
This oocyte has cleaved into two cells. But the cells vary widely in size. In the largest cell three nuclei are present (arrow). This suggests that the cells have chromosomal defects. Therefore this embryo is not good for transfer.
No. 7: Irregular cleavage
This embryo has cleaved into 5 cells. They are of very different sizes. The time-lapse analysis showed that it cleaved directly from 2 to 5 cells, because one of the cells cleaved irregularly into 3 daughter cells. This reduces the chance of pregnancy.