Once the eggs have been obtained through ovarian puncture in the genetic mother, fertilization is carried out in the laboratory with the sperm of a donor. This process can be carried out in a conventional way (IVF) by placing a sufficient quantity of sperm in contact with the egg or by introducing the sperm into the interior of the egg, which is known as intracytoplasmic sperm injection (IVF-ICSI).
In this way, after the union between the egg and the sperm takes place, embryonic development begins. The embryos are kept in culture in perfect conditions for 3-6 days and are observed to check that development occurs correctly.