The ICSI technique consists of microinjecting a spermatozoon into the egg. For this reason, it is usually called IVF-ICSI, since fertilization occurs in the laboratory. It is the technique of choice for those men who are diagnosed with a severe male factor since only the same amount of sperm is needed as that of the eggs to be fertilized.
In contrast, conventional IVF requires putting each egg into contact with a greater quantity of sperm and only one will be able to penetrate inside. In this case, it is not the embryologist who introduces the sperm, but it occurs naturally in the laboratory.