Embryo transfer: when and how is it done?

Assisted reproduction techniques that involve fertilization of the egg and sperm in the laboratory, subsequently require the transfer of the embryos to deposit them in the woman's uterus. This is the final step of an in vitro fertilization (IVF) treatment, either conventionally or by intracytoplasmic sperm injection (IVF-ICSI).

The symptoms after an embryo transfer will depend on each woman. Therefore, the presence or absence of discomfort when transferring one or two embryos is not an indication that IVF has been successful or not.

What is embryo transfer?

Embryo transfer consists of depositing the embryos generated in the laboratory in the woman's uterus, waiting for them to implant and give rise to a pregnancy. It is a simple and painless process that does not require anesthesia.

Normally, the embryo transfer is carried out in a room attached to the laboratory to avoid risks in the handling and transport of the embryos.

Embryo transfer characteristics

The success of the embryo transfer does not only depend on the quality of the embryos, but it is also important to assess the state and receptivity of the endometrium. In addition, the technique must be correct and they always have to check in the laboratory that the embryo has not remained in the transfer cannula.

When is the transfer made?

The day on which the embryo transfer should be carried out is decided by the specialists analyzing each case individually. It is important to take into account the number of embryos, their quality, the state of the endometrium and the results of previous IVF cycles.

There are centers in which it is transferred in the zygote stage, on day 2 of embryonic development or in the morula stage. However, the most common practice today is to carry out the embryo transfer on day 3 (in the early embryonic stage) or on day 5 (in the blastocyst stage). Despite this, both moments to carry out the embryo transfer offer their advantages and disadvantages.

What day is the embryo transfer performed?

If you want more detailed information on this topic, you can access the following article: Day 3 vs. Day 5 Embryo transfer.

Types of embryo transfer

Sometimes, the embryo transfer is not carried out at the same time as fertilization in the laboratory and the embryos are vitrified without altering their quality. For this reason, two types of embryo transfer can be distinguished according to whether the embryos are frozen or not:

• Fresh transfer: the embryos are fresh and are transferred in the same cycle in which they were created, without being frozen.
• Frozen transfer: The embryos are frozen for transfer in another cycle. This transfer is also called cryo-transfer or frozen embryo transfer. This type of transfer is used when it cannot be transferred in the same cycle in which the puncture was performed. An example in which this transfer is necessary is in the case of ovarian hyperstimulation.

Embryo transfer types

For more information on when and how the frozen embryo transfer is done, access this article: How Does the Frozen Embryo Transfer (FET) Procedure Work?

Embryo transfer Step by Step

As we have already mentioned, embryo transfer is a simple procedure in which the embryos are deposited at the bottom of the mother's uterus using a fine transfer cannula. Generally, this procedure is done ultrasound, that is, using an ultrasound to place the embryos in the right place.

In more detail, the process of embryo transfer to the uterus consists of the following steps:

• A sterile speculum is placed in the vagina
• The vagina is cleaned with physiological saline solution
• The cervix is cleaned with culture medium and cervical mucus is aspirated
• The embryos are placed in the catheter
• The catheter is inserted vaginally through the cervix till it reaches the uterus
• The embryos are gently placed in the uterine fundus
• The catheter is removed gently and slowly from the vagina

Embryo transfer for in vitro fertilization

The embryo transfer process lasts a few minutes and does not require sedation. The patient may feel slight discomfort, but it does not hurt. Only if the transfer is difficult, that is, if the gynecologist finds it difficult to introduce the catheter through the cervix to the uterus, can it be painful for the patient. In these cases, the type of catheter can be changed to see if it is possible to reach the uterus more easily.

Once the embryo transfer has been carried out, the patient rests for 20-30 minutes.

Afterward, the woman can return home leading a normal life, but without excessive physical effort, until the pregnancy test is performed 12-15 days after the embryo transfer. This period of time is known as beta-waiting and is usually quite distressing for most patients.

Embryo transfer medications

When it comes to performing an embryo transfer, there exist two possible options:

Natural cycle

Without using artificial medication or just with progesterone supplements. IVF/ICSI cycles are rarely done without progesterone.

Stimulated cycle

Using hormonal medications. Estrogen and progesterone are used to prepare the endometrial lining.

Embryo transfer in natural or substituted cycle

Medication should be administered both before and after the embryo transfer, following the doctor's instructions at all times.

Tips for the embryo transfer day

The following are some recommendations for the day of the embryo transfer:

Come in with a full bladder

It eases the transfer process to a large extent. With an empty bladder, inserting the catheter may become more challenging due to the input angle that forms.

Just relax

If your muscles are tense, the process becomes easier. When patients are too nervous, a muscle relaxant may help.

Don't use perfumes, lotions or nail polish

These chemical products should be avoided, especially at the operating room, transfer room, and the lab, since they are toxic for the eggs and embryos.

Recommendations before embryo transfer

Contrary to common belief, fasting is unnecessary—an embryo transfer is not a surgical procedure.

Tips for after embryo transfer

On the other hand, some advice for the patient after the embryo transfer is as follows:

• Rest at the clinic for 20-30 minutes
• Avoid immersion baths to prevent infections
• Continue with normal lifestyle avoiding excessive efforts
• Drink plenty of water
• Abstain from sexual intercourse until pregnancy test day

Recommendations after embryo transfer

In any case, it is always advisable to consult a specialist if there is any doubt.

In the following article you will find everything you need to know about how to act after an embryo transfer: Post Embryo Transfer Tips & Precautions – What Should You Expect?

Cancel embryo transfer

There are times when the embryo transfer must be canceled, either because no embryo has developed or because the endometrium is not ready for implantation.

The main reasons that can cause the absence of embryos in an IVF cycle are the following:

• Fertilization failure: does not fertilize any ovule, so there are no embryos.
• Arrest of embryonic development: it is produced by some genetic or developmental alteration of the embryo. The block in embryonic development is more common when a long culture is done until the blastocyst stage.

In these cases, a new IVF cycle should be started to try to obtain viable embryos for transfer.

reasons for cancelling embryo transfers

If, on the other hand, the transfer is canceled because the endometrium is not ready to allow implantation, the embryos obtained are frozen and transferred in another cycle, that is, a deferred transfer is made.

If you want to continue reading more in-depth about this topic, you can access this article: IVF Cancellation Reasons - What Happens If IVF Cycle Is Cancelled?

Quality and origin of the embryos

When higher quality embryos are transferred, they will have greater implantation potential and therefore pregnancy will be more likely to occur. The 4 main grades in which embryos are classified according to their quality are listed below:

• Category or grade A embryos: they are of the highest quality.
• Category or grade B embryos: they are of good quality.
• Category or grade C embryos: they are intermediate quality embryos.
• Category or grade D embryos: they are poor quality embryos and the probability that they will implant is very low.

Embryo grading

It should be noted that, in the event that the embryos come from donor eggs, they are usually of good quality and have a high probability of implanting.

In this link you will find detailed information on the classification of embryos according to their quality and implantation potential: Embryo Quality & Grading.

How many embryos to transfer

Most fertility clinics recommend single or two embryo transfers in order to reduce the probability of multiple pregnancy. In any case, however, determining the amount of embryos to transfer is not easy, since it depends on several factors, among which we highlight the following:

• Age of the patient
• Embryo quality
• Characteristics of the uterus
• What is causing infertility
• Embryo cryopreservation methods effectiveness

How to decide the number of embryos to transfer?

There is an increasing number of specialists that recommend single embryo transfers in order to reduce the chances of getting pregnant with twins or more. It should be reminded that this type of pregnancy carries a number of risks for both the mother and the babies.

Read this next: How Many Embryos Should You Transfer for IVF?

What is the fate of unused embryos?

Only the embryos considered optimal under the embryologist's criteria are used for the transfer. However, there may be top-quality embryos that are not used, in which case they will be cryopreserved (frozen) indefinitely. Thanks to this, they can be used in subsequent cycles.

If pregnancy occurs and the woman wants to have more children in the future, these cryopreserved embryos can be used for a new IVF cycle. The main advantage is that she would not have to start a complete IVF cycle again, but just take the medications that are necessary to prepare the endometrium for a new transfer.

There are cases where the patient or couple does not wish to have more children. The spare embryos can be donated to other couples or for stem cell research as long as they agree to sign an informed consent.

Fate of non-used embryos

In some countries like Spain, embryos cannot be destroyed until the woman's reproductive years have come to their end, that is, at age 50 approximately. In other words, if she does not want to use them or donate them, she will have to keep them stored in liquid nitrogen.

Click here to read more: What Is the Fate of Unused IVF Embryos?

What is the cost of a FET?

A FET is the option of choice when a patient needs to do a second attempt after a failed cycle, or when she wishes to have a second child using the spare embryos from previous cycles.

The cost of a Frozen Embryo Transfer in the United States averages anywhere from $3,000 to $5,000 per cycle. In the UK, on the other hand, the common fee is £1,400.

Some clinics offer shared risk 100% refund programs for FET, which allow patients to pay a flat fee for unlimited FET cycles for as many frozen embryos as that patient may have available. This does not include the fees for medication, which usually range between $400 and $800.

FAQs from users

What are the advantages of transferring on day 5 compared to day 3?

Existing evidence shows that culturing embryos till stage 5-6 of development, we can increase the pregnancy success rates per fresh and frozen embryo transfer. This is due to the fact that the embryos to transfer or cryopreserve can be selected more properly, since blastocysts have a higher implantation potential. It also improves embryo-endometrial synchrony.

One should keep in mind that about 50 percent of viable embryos will arrest on day 3 of development. In other words, they will not make it to blastocyst stage.

Is it normal for an embryo transfer to take place without symptoms?

Yes, after the embryo transfer it is possible to have some of the symptoms mentioned or none at all, this depends on how it affects each woman. There are some women who claim not to have had any, even up to several weeks after the positive beta-hCG result.

Can I do sports after the embryo transfer?

In the days following the transfer, it is important to avoid activities that involve lifting excessive weights and require significant abdominal pressure (for example: heavy shopping, carrying suitcases...).

Intense physical exercise such as swimming, running, spinning, aerobics, etc. should also be avoided until the pregnancy test has been performed.

It is normal to feel some abdominal discomfort, such as pre-menstrual pain, without this meaning a better or worse evolution of the cycle. Sometimes these discomforts may be accompanied by light bleeding, which should not be a sign of alarm.

How long should I wait to try again after a failed transfer?

It is not necessary to leave cycles of rest between transfers, a new attempt can be made in the following cycle. As long as the doctor considers it appropriate, after a transfer with a negative result, treatment with hormonal medication will be started to prepare the endometrium again for another transfer.

If embryo transfer is done with hatching does it increase the probability of success?

It has been observed that assisted hatching improves implantation rates in cases where the patient has had several unsuccessful IVF attempts or a frozen embryo transfer is performed. Therefore, hatching is not done in a generalized way, only in those cases in which it is considered that it can be beneficial.

How many embryos are implanted?

The number of embryos that manage to enter the endometrium will depend mainly on how many embryos have been transferred, their quality and the receptivity of the endometrium.

Thus, the fact that two embryos are transferred does not necessarily mean that a twin pregnancy will occur. It is possible that both will implant, but it is also possible that only one or even none of them will implant.

If the quality of the embryos is good (type A or B embryos), the probability of implantation will be higher. In these cases it is recommended to transfer only one embryo to avoid multiple pregnancies.

When does implantation of the fertilized egg occur?

Embryos implant on their sixth or seventh day of development, that is, 6-7 days after fertilization. Therefore, if the embryos are transferred on day 3, they will have to continue developing for a few more days in the uterus until they can implant.

On the other hand, if they are transferred on day 5, they will have already reached the blastocyst stage necessary for implantation to take place and will be able to begin to establish contact with the endometrium.

Recommended readings

As we have mentioned, a fundamental step for embryo transfer is the preparation of the endometrium. If you want to know how it is done, do not forget to visit the following article: Preparation of the endometrium for embryo transfer.

On the other hand, there is another modality of transfer, the zygote intrafallopian transfer or ZIFT, in which the fertilized eggs (zygotes) are introduced into the fallopian tube. You can find more information about ZIFT in this article: Zygote Intrafallopian Transfer - Advantages and Disadvantages