IERA Lisboa

IERA Lisboa

The Instituto Extremeño de Reproducción Asistida (IERA) was created to serve these couples using the most advanced medical and biological techniques and the most personalized treatments. 

The fertilization process is defined as the fusion of the female and male gametes, to give rise to the zygote, that is, the first stage of embryonic development.

Fertilization is a physiologically complex process that takes place over a period of approximately 18 hours. Naturally, it occurs in the tubes, making it necessary for sperm to reach this region of the female reproductive system after ovulation has occurred. It is estimated that under physiological conditions, between 500 and 1000 sperm are needed to fertilize the oocyte.

The basis of "in vitro" fertilization is to mimic in the laboratory the process that occurs naturally in the tubes. For this, the oocytes, or, to be more precise, the oocyte-cumulus complexes, are placed in culture plates with fertilization medium and incubated with an appropriate concentration of sperm. The spermatozoa induce the natural disagreement of the cells that surround the oocyte (cumulus cells) and initiate the first post-fertilization events. Between 18-22 hours after fertilization, oocytes are transferred to a new culture medium (without sperm) and the presence or absence of the female and male pronuclei is evaluated under a microscope. The observation of these two nuclei confirms that the fertilization was carried out correctly.

When the number of recovered mobile sperm (REM) is low, the in vitro fertilization process described in the previous section is not efficient. In such cases, a more specialized fertilization technique should be used, which uses micromanipulation techniques to inject a sperm directly into each oocyte. In order to be able to perform this procedure, the oocytes must be denuded, that is, it is necessary to remove the cells that surround them - cumulus oophorus, through enzymatic methods with hyaluronidase. Once denuded, they are placed in microdroplets and using an inverted microscope, the oocytes and spermatoids are micromanipulated, using suction and injection needles. With this technology it is thus possible to introduce a single sperm into the oocyte, crossing the pellucid zone (protective film that covers the oocytes) and the plasma membrane. Although this technique may seem more invasive, it does not interfere with the normal development of the embryo.

Once the oocytes are micro-injected, they are placed back in culture plates appropriate for the Time Lapse advanced visualization system, which allows the presence of the pronuclei to be verified without disturbing the zygote (fertilized oocyte). The ICSI percentage of fertilization is similar to that described for conventional IVF and is between 70 and 80%.