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Nov 23, 2022
3 min read

Fertilisation and embryo development

After our successful oocyte (egg) retrieval and semen collection we can finally start the next stage of IVF - the fertilisation!

The whole fertilisation process that happens in the embryologist’s lab is incredibly fascinating to me. First of all, the embryologist has to find the oocytes in the follicular fluid, which was collected from the follicles during the oocyte retrieval. The doctor has only a few minutes for this process because the oocytes do not tolerate the change of their environment well. The oocytes, are then transferred to an incubator, which provides the perfect conditions for growth - the incubator simulates the womb. At the same time, the oocytes are cleaned from other cells to make sure that there aren’t any disrupting elements during the fertilisation of the oocyte.

By the end of the procedure, we had three mature oocytes ready to be fertilised. In our case, two out of our three fertilised oocytes were developing properly in the laboratory. We have to understand that nature also plays a role in this process, even though it is happening in a controlled environment. If there is a genetic problem with the oocyte or the sperm, nature intervenes, which, in my opinion, is the way it is supposed to be

On day three after the oocyte retrieval, the doctor let us know the great news: we had two beautiful, well-developed embryos that were patiently waiting and looking forward to returning to their mother's uterus.

A similar procedure must be applied to the semen as well. The process of filtration chooses semen with the best motility (movement) and morphology (shape). After careful selection, the semen are washed from residual seminal fluids. Following the preparations, the embryologist selected the three finest sperms from the remaining sample. Each of these three sperms were injected into one of our three oocytes. This is a simplified version of how fertilisation is done.

The direct injection of sperm into an oocyte is called ICSI, or intracytoplasmic sperm injection. This protocol is mainly used when the sperm count, shape or movement are deteriorated and the sperms need a little help from the embryologist to increase the chances of fertilisation. Personally, I would have preferred to do this process the way nature intended to, meaning, let the thousands of sperm swim towards the oocyte in the culture dish and let the strongest one achieve the goal of fertilisation. Nevertheless, in our case doctors recommended ICSI as the method with the highest probability of success.

After fertilisation the oocytes are moved back into the incubator, which provides an optimal environment for their development. If everything goes according to plan, the fertilised oocytes will begin to divide. After the first 20 hours they undergo a thorough screening process during which the embryologist examines the oocytes to check for signs of fertilisation. Later, about 48 hours after ICSI, the oocytes are checked again. It takes up to 5 days until the embryologist can tell for sure if and which oocytes are fertilised.

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