An alternative solution to embryo transfer is for it to take place on the fifth day after the egg retrival when the embryo has reached the blastocyst stages. This prolonged culture of embryos in the laboratory offers some advantages compared to the embryo transfer of the third day. However, there are criteria for the selection of the method in a specific case event, as well as negative consequences, if used in all cases without any exceptions.
Advantages compared to the third day of embryo transfer
It is associated with higher success rates. By leaving the embryos to grow in the laboratory it is easier to choose the healthiest embryos, whose development has progressed. The transfer of blastocysts presents a success rate of 50% compared to the proportion of the third day embryo transfer, which lies aroung 35%.
Selection criteria for blastocyst transfer
This method is usually chosen when:
The disadvantages of blastocyst transfer on the 5th day:
Approximately 50% of embryos fail to reach the blastocyst stage and die before that.
When we have a small number of embryos there is the chance that an embryo transfer may not take place, if none of the embryos reaches the blastocyst stage.
Generally, the question on whether the embryos could have presumably evolved had they been transferred to their natural environment (uterus) sooner (3rd day) has not yet been answered. The choice for the day of embryo transfer and the embryo stage should be made upon evaluation of all parameters, both from a medical and an embryological point of view. The choice of the blastocyst stage for the embryo transfer can have significant advantages, but could lead to an undesirable result when used in appropriate cases.