By Dr. Llanos Medrano. Article updated and medically reviewed on 27/10/2026 by Manuel Izquierdo (Licensed Gynecologist – 280308601).
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.
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.
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.
This approach minimises the risk of multiple pregnancy and the complications associated with it. Transferring two embryos does not guarantee a higher chance of a healthy birth. Although it may increase the likelihood of pregnancy in certain circumstances, it also raises the risk of a multiple pregnancy, so the benefits and risks of each approach must be carefully weighed before making a decision.
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.
In order to select the best embryo our embryologists make decisions following a series of criteria such as:
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.
IVF-Life embryologists monitoring embryos with time-lapse.
Techniques such as time-lapse, the endometrial receptivity test and preimplantational genetic test (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.
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.
When pregnancy does not occur after the first transfer, it is common to wonder whether transferring two embryos on the next attempt could improve the chances of success. However, having had an unsuccessful transfer does not necessarily mean that transferring more than one embryo is advisable. Before making this decision, it is important to consider factors such as the patient’s age, embryo quality and development, previous treatments and possible reasons why implantation may have been difficult.
Current recommendations from the European Society of Human Reproduction and Embryology (ESHRE) prioritise single-embryo transfer to reduce the risk of multiple pregnancies and their complications. In many cases, transferring embryos one at a time and vitrifying the remaining embryos for use in later cycles can preserve good cumulative chances of achieving pregnancy and the birth of a healthy baby. The most appropriate approach should be assessed individually, taking each patient’s reproductive circumstances into account.
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.
In fact, this is the preferred strategy in assisted reproduction, particularly when good-quality embryos are available. The aim is to minimise the risk of multiple pregnancy and support a pregnancy with fewer complications for both mother and baby.
Embryo imaging for embryo transfer - IVF-Life Laboratory
Although transferring two embryos may be considered in certain circumstances, the decision should be based on an individual assessment. The patient’s age, previous attempts or the absence of preimplantation genetic testing are not, in themselves, sufficient reasons to recommend transferring two embryos.
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:
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.
Our policy is not to transfer more than one embryo if it is genetically tested. At our fertility clinics in Spain 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.
You can resolve your doubts and learn more about new fertility methods that are completely suitable for you by contacting us now.
ESHRE Guideline Group on the Number of Embryos to Transfer.
ESHRE guideline: number of embryos to transfer during IVF/ICSI.
.
2024;
647-657
Guía basada en la evidencia sobre los factores clínicos y embriológicos:
https://doi.org/10.1093/humrep/deae010
Kamath MS, Mascarenhas M, Kirubakaran R, Bhattacharya S.
Number of embryos for transfer following in vitro fertilisation or intra-cytoplasmic sperm injection.
.
2020;
CD003416
Revisión sistemática Cochrane que compara diferentes estrategias de transferencia embrionaria:
https://doi.org/10.1002/14651858.CD003416.pub5
McLernon DJ, Harrild K, Bergh C, Davies MJ, de Neubourg D, Dumoulin JCM.
Clinical effectiveness of elective single versus double embryo transfer: meta-analysis of individual patient data from randomised trials.
.
2010;
c6945
Metaanálisis de ensayos clínicos que compara la transferencia electiva de un único embrión:
https://doi.org/10.1136/bmj.c6945
Gardner DK, Vella P, Lane M, Wagley L, Schlenker T, Schoolcraft WB.
Culture and transfer of human blastocysts increases implantation rates and reduces the need for multiple embryo transfers.
.
1998;
84-88
Estudio sobre el cultivo y la transferencia de blastocistos humanos y su relación con las tasas de implantación:
https://doi.org/10.1016/S0015-0282(97)00438-X
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