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Embryo transfer is the final stage of the in vitro fertilization (IVF) process. If fertility treatment is successful, a positive pregnancy test 15 days later will confirm that pregnancy has finally been achieved.

The choice of embryo transfer day depends on the evolution of the entire IVF process in general. The specialist is in charge of determining if there are more advantages to transfer in day 3 or day 5 of embryonic development.

Currently, the tendency is to transfer a single embryo in the blastocyst stage in order to avoid multiple pregnancies. This is on the fifth day of embryonic development and the probability of implantation is higher.

Next you have an index with all the points that we are going to treat in this article.

Index

When to transfer embryos? On day 3 or day 5?

• 1. What is embryo transfer?
• 2. Embryo transfer on day 3
• 2.1. Advantages of day 3
• 2.2. Disadvantages of day 3
• 3. Transfer of blastocysts on day 5
• 3.1. Advantages of day 5
• 3.2. Disadvantages of day 5
• 4. Customize IVF treatment
• 5. Questions from users
• 5.1. When is an embryo transfer done on the sixth day?
• 5.2. Is it advisable to transfer two embryos of good quality on day 3?
• 5.3. Can embryo transfer be done on the fourth day?
• 6. Recommended Reading

What is embryo transfer?

Embryo transfer involves the deposition of the fertilized embryo or embryos in the laboratory within the maternal uterus.

In view of this moment, the specialist responsible for the treatment of assisted reproduction must take 2 important decisions when initiating the whole process:

Number of embryos to be transferred Spanish legislation allows a maximum of three embryos although recent research is focused on the single transfer to avoid multiple pregnancy, associated with increased fetal and maternal risk. Better day to transfer the embryos can be transferred any day, from the day 1, in which it is verified that there has been fertilization, until day 6 or 7. However, generally the transfer is done in day 2-3 or in day 5-6, since they are the moments in which it is most easily possible analyze their quality.

Next, the reasons that lead to the transfer on day 3, as well as those that decant the balance towards day 5 are detailed.

The controversy in this sense is wide, as there are several studies that show that it is better to transfer in day 3 and others that indicate that the success rates are greater in day 5.

Most experts bet on the personalized transfer, that is, choose the day of the transfer depending on the situation of each patient.

Embryo transfer on day 3

In a natural pregnancy, fertilization takes place in the fallopian tubes and it is not until the day 5-6 when the embryo reaches the uterus and implantation occurs in the endometrium.

However, when pregnancy is sought through assisted reproduction, the embryos are cultured in the laboratory with a different environment than can exist in the female reproductive tract. For this reason, it has always been tried to reduce the number of days of embryo culture.

The advantages and disadvantages of the transfer on day 3 are discussed below:

Advantages of day 3

The main advantage of early embryo transfer is that there are more embryos available.

As the days of cultivation pass in the laboratory, some embryos stop their development and are no longer viable. This is one of the reasons why some embryologists prefer to transfer on day 3, when the embryo has between 6 and 8 cells.

Therefore, the risk of cancellation of the transfer is lower on day 3 than if the embryos are left in culture until days 5 or 6. In addition, another advantage is that the number of embryos for vitrification is greater and can be used for future embryonic transfers .

Transfer of embryos on day 3

Disadvantages of day 3

The morphological parameters used to measure the embryonic quality at day 3 are not sufficient to be able to select the embryo with greater probability of implanting.

Although in principle the embryo with the best characteristics has been chosen, there is no evidence that it will not stop equally in the uterus after its transference and, therefore, there is a certain risk that this embryo was destined to degenerate and not implant.

The time when the embryo passes from cell stage (day 3) to blastocyst (day 5) is a delicate change that may compromise its viability.

Since with the transfer of a single embryo we run the risk that it will not be able to continue its development in the uterus, the usual practice is to transfer two or even three embryos on day 3. This means a high possibility of obtaining a multiple pregnancy with all the associated risks for the mother and the future babies that this entails.

Transfer of blastocysts on day 5

Sequential culture consists of keeping the embryos up to 5 days in the laboratory, at which time they become blastocysts. This is a little more complicated since you have to take into account your metabolic requirements, which change from day 3.

As in the previous case, the transfer on day 5 has a number of advantages and disadvantages:

Advantages of day 5

When a large number of embryos are obtained after fertilization, keeping them in sequential culture is a good option. This allows a natural selection of the embryo with greater capacity of implantation since most chromosomally abnormal embryos are not able to reach the greater stages of development.

On the other hand, the morphological selection of the embryo at day 5 is more accurate than at day 3, since the morphological parameters of the blastocysts have a better correlation with the embryonic quality.

Assessing the embryo's daily life according to certain morphological and morphokinetic parameters allows a more specific selection of the embryo with greater implantation potential.

The transfer of blastocysts also allows a better synchronization with the endometrium, since the embryos do not implant in the uterus before day 5 of natural way. Thus, there is greater endometrial receptivity.

Finally, to be able to select more accurately the embryo with greater capacity of implantation allows to realize a unique transference without lowering the rate of success and avoiding the multiple pregnancy.

Single embryo transfer

Disadvantages of day 5

Despite all the advantages, there is a risk that genetically normal embryos can not reach the blastocyst stage because of the culture conditions in the laboratory.

Under natural conditions, the embryo descends into the uterine cavity on day 4 of development and is in direct contact with endometrial cells that secrete molecules for their nutrition. Therefore, it is necessary to establish the optimal culture media and the conditions of temperature, humidity and light adequate to favor the growth of the embryos.

The main drawback of sequential culture is the risk of cancellation of embryo transfer, especially if few eggs are obtained after follicular puncture.

Customize IVF Treatment

Regardless of the preferences of each professional in defense at one time or another, all embryologists and assisted reproduction specialists agree that each treatment should be individualized.

It is important to choose the time of embryo development most appropriate for the transfer depending on each patient and the conditions of each situation of infertility. Some of the aspects that are valued are the following:

• Number of embryos obtained
• Embryonic quality
• Characteristics of previous IVF cycles
• Complementary techniques: DGP, ovodonación, ERA test ...
• Laboratory Conditions

In the case of IVF with PGD, the embryo biopsy is usually done on day 3 and the genetic analyzes take about 24-48 hours to obtain the result. Therefore, the embryo transfer is performed on day 5-6 when the embryos have reached the blastocyst stage.

In IVF with ovodonation, the trend is sequential culture and transfer at day 5 because there are always a higher number of embryos and good quality. The success rates of single transfers are the highest.

Finally, if there are problems with endometrial receptivity and an ERA test is performed, the embryo transfer will take place at the most favorable moment of the implantation window, as indicated by the test.

In Assisted Reproduction ORG you have the option to get a free first visit so that you go to inform the clinic of the best treatment for you. We have obtained agreements with Spanish centers to offer you the best discounts. You have all the information here: See discounts in FIV / ICSI.

User questions

When is an embryo transfer done on the sixth day?

When it is decided to make a sequential culture and the embryos evolve to the blastocyst stage, the embryo transfer usually takes place on day 5. However, there are cases in which the embryonic development goes a little slower and it is necessary to wait until the day 6 to be able to assess better the quality of blastocysts.

Is it advisable to make a transfer of two embryos of good quality on day 3?

The best day for the transfer should be assessed according to each patient as discussed in this post. On the other hand, if the specialist has determined that it is better to transfer 2 embryos instead of one, day 3 offers more advantages since there is no risk of cancellation due to being left without embryos.

Can embryo transfer be done on the fourth day?

It is not recommended to make the embryo transfer on day 4 because at this time the embryos are in a morula state. It is difficult to determine the embryonic quality of the morulae and, therefore, we will not know which one is more likely to lead to an evolutionary pregnancy.

On the other hand, there are some cases in which it is transferred on day 4. For example, when embryos are thawed on day 3 and they want to stay one day in culture to see if there is survival.

Recommended Reading

Currently, a series of morphological and morphokinetic criteria are considered to choose the embryos to be transferred. You can get more information about this in the following post: Embryonic quality for transfer.

Single embryo transfer is a practice that is being implemented in all clinics worldwide for patients with no serious fertility problems. In any case, each patient is different and their treatment must be adapted according to the possibilities. In the following post we discuss this topic more in depth: How many embryos must be transferred?

Once the embryo transfer is done, the waiting period begins until it is time to perform a pregnancy test. In the following article you can continue reading on this topic: Symptoms of implantation of the fertilized egg.