Fertilisation failure
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 make a normal pregnancy. In the following we will give a few examples of eggs which are not top quality or not suitable for transfer back into the uterus.
Eggs No 1 is not properly fertilized. It has only a single pronucleus, and thus presumably only 23 chromosomes instead of 46. Such eggs may well begin to cleave, although their content of chromosomes is not correct. But they give no pregnancies, and hence are not put back in the womb.
Egg No. 2 contains 3 pronuclei. 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 egg has been fertilized by 2 sperm cells (this
is due to an error in the egg 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 fertilization.
Some eggs can not fertilize (No. 3). The reason is usually that they were immature. Oocytes from small follicles are more likely to be immature.
Photo No. 4 shows an egg which has become atretic. Although it resembles an egg, the cell is dead and unable to be fertilized or cleave.
Eggs No. 5 has two pronuclei, however, it 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.
Inappropriate cell division
The oocyte (No. 6) has cleaved into two cells. But 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 into the womb.
Egg No. 7 have split into 5 cells. They are of very different sizes. This reduces the chance of pregnancy.