Day 0: Egg retrieval, washing the sperm sample and fertilisation of the eggs
The doctor retrieves the eggs which are delivered along with their associated fluid to the biomedical laboratory technician at the laboratory. Eggs are found through close examination of the fluid using a microscope. The laboratory microscope is fitted with a video camera which will allow you to see the eggs.
The eggs are placed in a dish containing a culture medium, after which they are stored in an incubator (a type of heated cupboard kept at 37°C), until they are to be fertilised.
16–18 hours after the eggs have been retrieved, you can see whether the eggs have been fertilised or not. On average, approx. 70-80% are fertilised. Normal fertilisation will show 2 nuclei. One is from the woman’s egg and the other from the man’s sperm cell. Pronuclei contain the chromosomes.
Occasionally, there are 3 nuclei in one egg. This means that faulty fertilisation has occurred in the egg and it contains one chromosome too many. In this case, the egg will be destroyed. The reason why faulty fertilisation sometimes occurs can be that 2 sperm cells have entered the egg at the same time, or that the egg has been “sick” right from the aspiration stage.
Days 2–3: Egg implantation and assisted hatching
2 days after egg retrieval, we examine the eggs, which should have divided into 2–4 cells. Once a fertilised egg begins to divide, it is called an embryo.
The laboratory evaluates the quality of the embryo. They do this by determining the number of cells, how rapidly they have divided, and how they have divided.
Day 2: 4 cells
Day 3: 8 cells
If an embryo develops normally, it will contain 2–4 cells on day 2, 6–8 cells on day 3, and approx. 100–150 cells on day 5. Now it is called a blastocyst. On day 5 or 6, the cells will break out of their surrounding shell, which is known as the zona pellucida. This process of the egg breaking through the shell and being released from the zona is known as “hatching”. This process is necessary to allow the egg to attach itself to the uterus firmly and allow a pregnancy to develop.
The function of the shell is to ensure that only one sperm cell enters the egg. By handling and cultivating the egg outside the woman’s uterus, it is believed that the egg’s shell becomes harder and more compact. This change can have an influence on the egg’s ability to break out of the shell and thus implant itself in the uterus. We can help this process along in the laboratory: Read more about assisted hatching.
Once the divided embryos have been given a score, the embryo(s) which will be returned to the uterus are selected. On the day before the egg implantation, you will be informed about the number and quality of the embryos chosen.
You will be able to follow the development of your embryos via video on an iPad.
The development of the egg – Day 3
If there are extra fertilised eggs once the implantation of the egg is complete, we will evaluate whether these eggs can be cultivated further. If the eggs develop into blastocysts, we can offer you the option of freezing them.
In accordance with current legislation, they can be frozen for 5 years. Not all blastocysts survive thawing. Blastocysts are thawed before implantation, so that we can evaluate whether they have survived the thawing process and are of sufficient quality to be implanted in the uterus.
Ciconia offers cultivation of the fertilised egg until the blastocyst stage; the final stage before the egg attaches itself to the uterus.
A blastocyst is an egg that has begun to develop 2 different cell types and a fluid-filled cavity between the cells, 5 days after fertilisation. The cells that are located just under the outer shell are the ones which develop into the placenta, and that small firm cluster of cells becomes the foetus.
On the 5th day, the blastocyst grows in size. This is because the cells that lie just under the egg’s shell pump fluid into the cavity. Thus the pressure increases so that the egg’s shell (zona pellucida) cracks open (hatches), so it can now attach itself to the uterus.