Currently, there is some controversy in the field of assisted reproduction regarding embryo transfer and the decision of whether to transfer a single embryo or more than one embryo.

At our fertility clinics in the IVF Life Group, we recommend the transfer of a single embryo, in order to reduce the risk of a twin pregnancy without reducing the chances of success. We spoke to Dr Estefanía Rodríguez Ferradas, Medical Co-Director and Research Director at IVF Donostia, to learn more about what the transfer of more than one embryo during fertility treatment entails.

Reproductive Medicine boosts pregnancies

In the last ten years, the number of children born to mothers over the age of 40 has increased by 63.1%. Delayed motherhood, coupled with the declining quality of male sperm, means that more and more couples are having to resort to reproductive medicine to conceive.

The use of such reproductive techniques is believed to be the reason for the increase in the number of multiple pregnancies, leading to high-risk pregnancies for both the mother and the babies.

More than one embryo equals more success in getting pregnant?

First of all, we must establish that the transfer of a single embryo does not significantly reduce the likelihood of pregnancy. It is also useful to understand the difference between “cycle” and “embryo transfer”.

If two embryos are transferred at the same time, the probability of success per transfer may be higher than for a single embryo transfer. However, if it is decided to transfer a single embryo, the patient will be left with frozen embryos that can be used for further transfers.

Therefore, at the end of the cycle and after having transferred the embryos necessary to achieve a pregnancy, the final success rate is equal or higher.

“Our recommendation is to transfer one embryo at a time at the blastocyst stage (day 5 development). This way, we minimise the risk of multiple pregnancies and the complications associated with it. In some recent studies, it has been proven that the transfer of several embryos at the same time does not improve the chances of pregnancy, but can actually decrease them in the case of an abnormal immune response. This type of response hinders the correct implantation of the embryo, and when more than one embryo was transferred, this response is enhanced and has an even greater impact on the embryos,” says Dr Rodríguez Ferradas.

Improvements in embryo transfer techniques

In the past, it was more common to transfer two or even three embryos. Nowadays, assisted reproduction techniques have been greatly improved, and it is very rare to transfer more than two embryos. At IVF-Life we only transfer one embryo as we always transfer embryos at the blastocyst stage.

How are the best embryos and the best time to implant them chosen?

In order to select the best embryo our embryologists make decisions following a series of criteria such as:

• The number and appearance of the cells that make up the embryo (morphological),
• The rate of cell division (kinetic).
• The chromosomal composition (genetic).

Thanks to technological advances, the tools embryologists use to assess these criteria have been significantly improved, resulting in better implantation rates and more healthy births following the transfer of a single embryo.

Techniques such as Timpe-Lapse, the Endometrial Receptivity Test (ER MAP) and Preimplantational Genetic Screening (PGS) assist in the continuous improvement in selecting the best embryo and choosing the optimal time for embryo transfer.

“In addition to embryo selection, we also have to take into account the endometrial factor. We cannot transfer an embryo at any given moment. In order to perform an embryo transfer, we must carry out a series of steps in order to prepare the uterus so that the embryo can implant correctly and remain “attached” for the entire duration of the pregnancy,” explains Dr Rodríguez Ferradas.

Are there cases where more than one embryo is transferred?

Each patient is unique and in every situation, there are certain conditions that we assess in our clinics. In the case of patients that undergo embryo transfer on the 2nd or 3rd day of embryo development, we assess with the patients which decision to make.

In this case, the transfer of two embryos can be performed with the assumption that only one of them will reach the blastocyst stage.

The risk of trasfnerring multiple embryos

When we talk about blastocysts, i.e. embryos, on the 5th or 6th day of development, which we know can implant and achieve pregnancy, we are always talking about the transfer of a single embryo.

Only in cases where there are specific reasons, such as not performing a preimplantation genetic study in patients who are over 35 and have a much lower rate of genetically good embryos, do we weigh the options together with the patient.

In that case, two embryos could be transferred assuming that one of them is not genetically healthy and would not result in pregnancy. The problem here is that if both embryos implant and the one that is not genetically healthy ends up miscarrying, it could put the other embryo that is genetically healthy at risk.

What to do with surplus embryos?

If more than one “blastocyst” embryo is obtained, there are several options available. On the one hand, the patient can opt for the vitrification of embryos intended to use them in future treatments. Thanks to current technology we can transfer one embryo at a time and freeze the other embryos for later use. In fact, treatments with “fresh” or frozen embryos obtain similar results.

When pregnancy has been achieved and the patients decide not to use the embryos in future assisted reproduction cycles, they can choose between the following options:

• Donation of embryos for reproductive purposes: There are cases of patients who, due to certain circumstances (single women, hereditary diseases, economic reasons…), decide to adopt embryos. With the help of other patients, who have taken the altruistic and admirable decision to donate their cryopreserved embryos, these patients will be able to fulfil their dream of establishing a family.
• Donation of embryos for research purposes: Another possibility is the voluntary donation of embryos to biomedical research, within authorised centres and authorised projects.
• Destruction of the embryos without further use: This will be the final fate if the embryos are not to be used and are not to be donated.

The differentiating factor lies in embryo selection

At IVF-Life we have come to the conclusion that a single high-quality embryo transfer should be performed whenever it is possible.

This way, we increase the probability of a successful transfer, due to the good embryo quality and also avoid the risk of multiple pregnancy.

Dr Rodriguez Ferradas concludes with “Our policy is not to transfer more than one embryo if it is genetically tested. At our clinics we consider that it is always better to transfer a tested embryo, to avoid a transfer of multiple embryos being a problem for the healthy embryo”.

The reality is that each case and each story is unique but at IVF-Life we work with cutting-edge technology and thanks to the work of our embryologists and doctors who take the right decision to achieve successful treatment, we will help you to get pregnant.

By filling out this form, you can ask any questions you may have and find out more about the fertility treatments that are suitable for you.