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This technique is similar to the "classical" In Vitro Fecundation previous to the laboratory phase, where the fertilization is carried out through the "Intracytoplasmic Sperm Injection" (ICSI). It is a process in which a single sperm is injected into the cytoplasm.
The sperm injection will be carried out in the eggs that present a correct ripeness (the 80% approximately), that is, those that we be found in Metaphase II. To do it we should free them of the cells that surround them. This process is known like “denudation”.
The microinjector consists of a reversed microscope (we can observe the eggs and the sperms with 400 increases) and two microinyectors arms. With one of them the egg is hold to the microinjector by suction, and with another hydraulic arm the sperm is captured and gets in the egg, facilitating thus the fertilization.
Later, the microinjected eggs are kept in the most similar conditions than the physiological ones. This is obtained keeping the eggs in an incubator, with a stable temperature of 37 º C and 6 % of CO2, until verifying their fertilization 16-18 hours after the microinjection.
Two or three days later (day + 2 ó + 3) since the fertilization, will be carried out the embryo transfer to the uterus. The non tranferred embryos can be cryopreserved (frozen) These embryos are stored in liquid nitrogen and can be thawed at a later date, to do a new embryo transfer without ovulation induction.
In both techniques, in the case we obtain a lot of embryos, they can be maintained in culture until day +5 or +6. when they became blastocysts , carrying out the transfer in day + 5 or + 6, permitting us a better embryo selection, and therefore a greater number of pregnancies.