Embryos enter in a phase which is called blastocyst 5-6 days after collecting the eggs. In this phase, embryos are consisted of two different groups of cells, an outer layer of cells surrounding the inner cell mass and a fluid-filled cavity which will form the placenta and inner cell mass which subsequently forms the embryo.
Image of a blastocyst at the 5th day (inner cell mass clustered inside and outer cell mass extending outside can be viewed).
Since a large number of quality embryos are achieved after the test tube baby, the embryos can be developed to this phase and transferred when test tube baby has failed for several times. This type of transfer is called “blastocyst transfer”.
Whether patient is convenient for blastocyst transfer is decided depending on the patient age, the number and quality of embryos, and patient’s previous attempt to a test tube baby. If a blastocyst transfer is decided upon the couple’s consent, embryos are kept longer in the laboratory environment to allow formation of blastocyst. The achieved blastocysts are transferred into the mother’s uterus at the 5th or 6th day. It is possible to select more quality living embryos as the embryos can be monitored longer in the laboratory environment. Although the chance of the embryos to live longer in a laboratory environment gradually increases depending on the technological developments in the medium, the chance of an embryo to reach the blastocyst phase is around 50% with many other factors, e.g. genetic factors.