Blastocyst embryo transfer

How the embryo naturally grow?

When a sperm fertilises an egg at the terminal part of the Fallopian tube (the tube that connects the ovary to the uterus), the resulting embryo develops from the original single cell into a complete human being, consisting of billions of cells. This occurs through a series of cell divisions into two cells, then four, then eight and so on.

By about four days after fertilisation, there is a ball of cells, which then absorbs fluid and expands to form a cavity. The embryo is now called a blastocyst and has about 120 cells. The blastocyst consists of a layer of outer cells that eventually become the placenta, and a small number of inner cells, which will form the fetus.
At this stage, about a week after fertilisation, the embryo has completed its journey down the Fallopian tube and reached the uterus. About this time the blastocyst hatches out of its thin shell (the zona pellucida) and implants in the womb lining.

When the embryo is usually transferred back to the uterus?

* In most IVF Units embryos are normally transferred 2 to 3 days after the egg collection. However in natural cycles embryos would not normally reach the uterus until day 5.

Why the embryo transfer is usually carried at Day 2/3?

Culture of embryos, in the laboratory, to the blastocyst stage was very difficult because the several culture media that were used to supply nutrients to the embryos were inadequate for extended embryo growth in the laboratory. Therefore, many embryos died before they developed into blastocysts. Recently, the use of sequential culture medium (the embryos are cultured in different media according to their stage of growth) has enabled a larger number of embryos to develop into blastocysts.

When the Blastocyst transfer is carried out?

**Embryo transfer will be dependent on the timing of development of the embryos. Some embryos develop faster to blastocyst than others. Development may also be different to previous cycles. Therefore transfer may take place on any day between day 4 and day 7 after egg collection, and patients must be available to have the transfer on any of these days.

Are success rates affected by the day of embryo transfer?

Pregnancy rates are different according to the day of transfer:

What are the advantages of blastocyst transfer?

- Better pregnancy rate.
- A blastocyst gives a better idea of the competence of an embryo and has a higher chance of implantation than a cleaved (day 2-3) embryo. The improved implantation rates following blastocyst transfer is due to selection of the best embryos. That does not mean that a pregnancy will definitely occur as other factors are also important such as the endometrial lining of the uterus

Avoid high-order multiple pregnancies.

Due to the fact that it is difficult to predict on day 3 which embryos are more likely to produce a pregnancy, four or more embryos are frequently transferred in hopes that at least one will result in a live birth. But that results into high-order multiple gestations (triplets or greater). In such pregnancies, there are considerable medical risks as well as financial and emotional considerations.
In blastocyst transfer, as the embryos implant better, only two or three embryos are transferred, practically eliminating the possibility of triplets or greater.

For whom blastocyst transfer is recommended?

-in general, blastocyst transfer is more advantageous for patients who develop a number of eggs and embryos. A significant correlation has been reported between the number of eggs and the number of blastocysts developed, as well as the number of day three embryos and the number of blastocysts developed.
-Patients who had repeatedly failed to achieve a pregnancy following the transfer of good quality cleaved embryos (If the embryo arrest and did not develop to blastocyst, this may indicate a potential egg problem)
-Patients who wish to achieve a pregnancy without the risk of multiple pregnancy, here the transfer of one blastocyst will be recommended.

What are the disadvantages of blastocyst transfer?

Because only a few embryos develop to the blastocyst stage, it is possible to have no embryos survive to day five to transfer. This is especially true if the cycle begins with only a few fertilized eggs. When no embryos survive to become blastocysts, it is a tremendous disappointment. The looming question then becomes, "Would the embryos that did not survive to become blastocysts have implanted if transferred at day three?" Unfortunately, we simply do not have enough clinical data at this time to answer that question. In our opinion, pregnancy would have been unlikely in that situation. But since that outcome is not a certainty, day three transfers is still be a reasonable option for some patients.

Is Blastocyst Culture and Transfer for Everyone?

Patients who have fewer oocytes retrieved, fewer fertilized or fewer dividing embryos by day three in culture have no advantage using blastocyst culture.