TTC Warrior Jennifer Jay Palumbo explains in simple terms….
Embryo transfer is an important part of the IVF process. After retrieving your eggs, an embryologist will combine them with sperm in vitro. Next, the fertilised embryos will be cultured in the laboratory.
Essentially, embryo culture is a selection process. Each embryo’s quality and maturity are evaluated for up to 3 or 5 days, after which the embryologist will decide which embryo is most likely implanted successfully.
However, determining the best day for embryo transfer has always been controversial. Even today, after extensive research, there is still uncertainty surrounding whether day 3 or day 5 transfer results in more successful implantations. In this article, we discuss the differences, pros, and cons.
The Difference Between a Day 3 and Day 5 Embryo
An embryo begins its life as a single cell. From here, it divides every 12–24 hours. The embryo will develop into a multi-cell embryo by the third day, comprising about 4–8 cells. Throughout day 4, the cell will continue to divide until it reaches the blastocyst stage on the fifth day. By this time, the embryo will have between 70 and 100 cells.
The embryo will contain two different cell types: the inner cell mass and the trophoblast. The inner cell mass will form the fetus, and the trophoblast will become part of the placenta. At this point, the embryo will have grown enough energy to activate its genes in a genomic activation process. This is a complex process that begins the development of the fetus.
Why Might a Doctor Recommend a Day 3 Transfer?
If there is a low number of good quality, dividing embryos on day 3, it may be clear to the embryologist which embryo to select for transfer. The embryologist may recommend transferring the embryo on day 3, as some research suggests the uterine environment can contribute to embryo growth and successful blastocyst development.
However, this is a controversial theory; some fertility specialists think the evidence suggesting that embryos develop better in the uterus is dubious. Furthermore, there is a risk that an embryo may stop growing after day 3. This is because it may turn out that the embryo is aneuploid, which means it does not carry the 46 chromosomes needed for a healthy pregnancy.
What are the Advantages of a Day 5 Transfer?
Many fertility specialists favour a day 5 transfer because it allows them to assess whether or not an embryo is chromosomally normal. In addition, they can identify and discard aneuploid embryos by waiting until the fifth day when the embryo reaches the blastocyst stage. This increases the chances of implantation and healthy fetus development.
Furthermore, waiting until this stage allows for other diagnostics. For instance, if the patient wishes to prevent the transmission of a genetic disease, waiting until day 5 will enable doctors to perform PGT-A. With this procedure, fertility specialists can select an embryo that does not carry the genes associated with the disease.
Day 5 transfer also allows doctors to check for any other underlying problems. For example, if no cleaved embryos advance to the blastocyst stage, there may be issues with egg quality or the prescribed fertility medicine. Either way, day 5 transfer allows doctors to make accurate assessments.
One concern associated with day 5 transfer is embryo survival outside the womb. However, little evidence suggests that the blastocyst is more vulnerable than any other embryonic stage.
It’s also important to note that if a patient has multiple embryos that all seem to be developing similarly, it might be impossible to choose which ones are the highest quality. When there is no clear distinction between embryos, it is best to wait until day 5 to perform embryo transfer. This allows your doctor to evaluate the embryos further and see which have reached the blastocyst stage.
Ultimately, every patient is different. Your reproductive endocrinologist will put together the protocol they think will best maximise your chances of a healthy pregnancy.