Vienna In Vitro Center, Sofia, Bulgaria > We can help > In vitro fertilization (IVF) > The fertilization - IVF or ICSI

Fertilization with IVF or ICSI

The basic steps for the fertilization of the ovum are: The egg cell has completed essential steps towards maturing in the hours before the extraction (meiosis). This is important in order to have the right amount of chromosomes (carriers of genetic information) while waiting for the sperm cell. This phase is known as metaphase II.

IMPORTANT: Only an egg cell, which has reached metaphase II can be fertilized! This phase will not be reached by all collected egg cells!

What different methods for fertilization exist?

A) The traditional technique of In vitro Fertilization (IVF)

Following the semen collection the sample is specially prepared in order to quickly isolate all the fast moving sperm cells and to make them “ready” for fertilization. At the end of this procedure they are placed in a special culture medium. The egg cells are located in a small bowl within the same medium. A drop of the sperm cell liquid is added to the egg cells. Independently, the sperm cells find their way towards the egg cells. In most cases, one sperm cell succeeds in fertilizing an egg cell. This technique can be applied, if

1) there is a sufficient amount of

2) fast moving sperm cells with

3) a normal external structure present within the sample.

Day 0 - IVF: Thousands of sperm cells on an ovum

A sufficient amount (at least 100,000 per egg cell) of sperm cells that are able to move fast, reach the egg cell and bind to the external shell (Zona pellucida). Normally, just one sperm cell manages to pass through this shell. On the day after the puncture (the day of puncture is called day zero and thus we now speak of day 1) it can be checked if any and how many egg cells have been fertilized. Afterwards, it is possible to identify the first and second “polar bodies” on the egg cell and in the middle of the egg cell the two so called “pronuclei”. In this delicate process of fertilization there are a lot of deviations from the regular state. This can make it more difficult to tell if the fertilization was successful. Hence, it is better to wait one more day: often a regular embryo develops.

B) The intracytoplasmic sperm injection (ICSI)

If there are not enough fast moving and normally structured sperm cells available, a fertilization via ICSI is offered. A sperm cell is injected into the egg cell via a micropipette.

In order to rate the quality of sperm cells and to make a decision which technique for fertilization to apply a semen analysis will be conducted.

IMPORTANT: Even if the sperm cells feature all the above mentioned characteristics and therefore no complications are expected, it might still happen that just a few or no egg cell is fertilized. This might be due to the egg cells' quality or the sperm cells suffer from a malfuntion that cannot be identified with contemporary techniques.

ICSI Movie here!


Day 0 - ICSI: 1 sperm cell is being injected

IMPORTANT: Please understand that we are not able to formulate a distinctive statement for some egg cells the day after the puncture.

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