After they are created in the IVF process, a selected number of specific embryos are transferred from the laboratory into the mother’s uterus. For a successful pregnancy and healthy baby the embryo or embryos must implant on the uterine wall. The term “blastocyst transfer” refers to performing this procedure at a specific time in the embryo’s development.
The question of when an embryo is transferred is important to the infertile couple’s IVF outcome. Typically, embryo transfer (ET) is performed around day three after fertilization. Embryos are considered to be at the blastocyst stage of development immediately prior to hatching, around five to six days after egg retrieval. There is increasing evidence that waiting until that stage of development to transfer results in higher implantation rates per embryo.
It is easier to choose healthier embryos for transfer when they are farther along in development.
Transferring to the uterus five to six days post-fertilization results in a uterine environment for the embryo that more closely resembles a healthy natural conception.
In effect, blastocyst transfer allows for the transfer of fewer embryos with a higher potential for implantation. This is an especially important point for infertility patients who want to take every possible step toward having a single healthy baby rather than a multiple pregnancy, which can cause serious complications and health risks to both mother and child.
Also, patients who are also using preimplantation genetic diagnosis (PGD) will be using blastocyst transfer. Embryos that are biopsied in the PGD process are grown to the blastocyst stage.
When blastocyst transfer is the chosen procedure, the patient will first be scheduled for embryo transfer on the third day after egg retrieval. On that day, the IVF lab staff will evaluate the embryos and if there are at least five high-quality embryos, the transfer will be rescheduled for Day 5.
There is a risk that none of the embryos will develop to blastocyst stage. On average, about half of fertilized eggs achieve the blastocyst stage. When there are no embryos to transfer as of day six, the distressing news might be tempered with the knowledge that the non-developing embryos would likely not have resulted in pregnancy if they had been transferred earlier.