Differences between embryo transfer on the second and fifth day

After either in vitro fertilization or ICSI treatment , most of the embryos obtained reach a stage suitable for transfer to the uterus, on the second day after oocyte retrieval.

However, many assisted reproduction centers transfer the embryos on the fifth day, when they are at the blastocyst stage.

The blastocyst stage usually occurs from the 4th to the 14th day after the formation of the zygote (which is formed by the fusion of sperm and egg).

The embryos are generally classified by the embryologist on the second day according to precise criteria which can vary from center to centre.

At the Genera center in Rom a, the classification of embryos at the 2-8 cell stage is based on 4 criteria:

– number of cells present in the embryo (growth rate)
– symmetry of the cells
– presence of anucleated fragments in the perivitelline space of the embryo
– identification of the nucleus (or any multinucleations) present in each cell

Advantages and disadvantages of the transfer on the second day

The advantage of transferring an embryo on the second day is the possibility of making only one passage in the culture medium which allows the survival of most of the embryos. Then the best ones are selected.

The disadvantage of the transfer on the second day is that in a normal menstrual cycle the embryo on the second day is not in the uterus but still along the tubes. Furthermore, the morphology is not always representative of the survival potential and therefore also the classification of the embryologist may not be very precise.

Advantages and disadvantages of the transfer on the fifth day

On the other hand, the advantage of the transfer on the fifth day is that the embryo is in a stage in which it also naturally reaches that stage in the uterus. The blastocyst stage also allows for a better selection of embryos as most of the “defective” ones stop its development between the second and fifth day.

However, this technique requires more passages in vitro and generally in this stage the supernumerary embryos do not survive freezing.

To avoid the risk that all the embryos fail to reach the blastocyst stage and therefore survive until the fifth day, many centers prefer to transfer on the second day.

How is the transfer performed?

The transfer does not require any anesthesia. Through a Cusco speculum, the cervix is ​​visualized which is carefully cleaned, and the embryos are transferred with a catheter.

There is still no common line on where to release the embryos. Most centers prefer to deliver mid-uterine cavity. This should be done under ultrasound monitoring for a more careful placement of the embryos.

Even though there is no chance that the embryos will “exit” the uterus, the patient is advised to lie on her back for about a couple of hours before going home. There is no evidence that this helps pregnancy but it certainly helps the woman psychologically.