The embryos that have been developed in the laboratory under strict quality conditions are selected to be transferred into the maternal uterus.
The day chosen for the embryo transfer is individualised in each specific case and although it is frequently performed on the third day of development, the transfer can be made from the second up to the fifth.
We have routinely transferred two embryos at CREA since January 2003, although the transfer of one embryo has became more and more frequent, mainly in couples who come back with a desire to have a second child.
The selection of the embryos does not exclusively depend on their condition on the day of the transfer, although this would seem logical, since after many years of experience it has been shown that their stage of development is more important.
At CREA we have designed a method of embryo evaluation based on the progress of development from the moment at which fertilization takes place up to the transfer or vitrification, thereby allowing us to select those with better implantation potential.
This evaluation method was made known at the National Congress of the Spanish Association of the Biology of Reproduction in 2003, and throughout these years it has shown its effectiveness in allowing improvement in the rates of implantation.