In this webinar session, Dr Jana Voborská Neudeckerová, IVF Specialist at Unica Clinic, discussed single embryo transfer and whether it is always the best option.
Dr Neudeckerová started by explaining the whole embryo transfer process in IVF process treatment. She also answered the question that is so often asked by patients: Is single embryo transfer always the best solution?
IVF process starts with the stimulation of the ovaries, which is done with FSH hormones and these hormones a woman needs to inject herself, and it starts on the second day of the menstruation bleeding. On about the 7th or 8th day of a period, an ultrasound checkup is performed to check how many follicles are growing, and how big they are. According to this ultrasound, it’s possible to plan an egg retrieval. It is a short surgical procedure under general anaesthesia, during this procedure the ovaries are punctured, the follicle fluids are taken, and in the follicle fluids, the embryologists will find matured eggs, and only those will be fertilized. After 5 days of embryo development, at the blastocyst stage, embryo transfer is performed.
The embryo transfer procedure is simple, painless, and takes about 5 minutes. It is one of the key steps in the IVF process. During this procedure, the embryo is inserted into the uterine cavity with ultrasound to be sure that the catheter is inside the uterus, the embryo will be put correctly, and after 2 weeks, the woman will do the pregnancy test, and hopefully, with a positive result. This is how it works in a fresh transfer.
However, if it’s not the first transfer and we have to do a frozen embryo transfer, no needles or injections are needed, and oral or vaginal tablets of oestrogens and progesterone are used for the transfer. At the beginning of the cycle, we start with using oral oestrogens, around the second day of the period, we will do the ultrasound checkup of the endometrium, and if the endometrium is in optimal condition and is trilaminar and if it is about 7 or more millimetres high, then we can plan the embryo transfer.
The first division of the embryo occurs on day 3 of embryo development (morula stage), but at this stage, it is still too early to determine the potential of this embryo to implant. Many of the embryos on day 3 may be of similar quality, and that is why it is difficult to see which ones are the most promising. Therefore, it is better to allow the embryos to develop further and observe which embryos can reach the blastocyst stage. The embryo transfer of blastocyst, day 5 of the development, has the best potential.
It’s possible to transfer 1 or 2 embryos. Double embryo transfer doesn’t double the chance of pregnancy, the chance is higher, and if you transfer 2 embryos, there is a high risk of multiple pregnancies. These can cause a higher risk of miscarriage. Recent studies suggest that sometimes when one embryo is healthy and the second embryo has some, for example, genetic issues, it could influence the other embryo and cause a miscarriage. Endometrium behaves differently toward healthy and unhealthy embryos. Other risks involve preterm birth and low birth weight, also, pre-eclampsia, higher blood pressure, and intrauterine growth restriction of the fetus. Therefore, experts recommend transferring just one embryo at a time.
Studies regarding single embryo transfer show that after a single embryo transfer, the chance of live birth is 33%, if you do a double embryo transfer, it’s higher, it’s 46%. However, if we look at multiple pregnancy outcomes, in single embryo transfer, it’s 16%, while in double transfer, it is almost 17%, and the chance of pre-term birth with double embryo transfer is quite high, it is 31%. The risk of low birth weight is also nearly 30%. These are the reasons why single embryo transfer is recommended.
EmbryoGlue -is a special medium designed to transfer embryos directly to the uterus. It gives a higher chance of implantation, it increases the chance of pregnancy by about 4-5%.
PGT-A (Preimplantation Genetic Testing for Aneuploidies), and PGT-M (Preimplantation Genetic Testing for Monogenic disorders), its genetic examinations of the embryo before embryo transfer, it’s possible to do it only in the blastocyst stage of development. The embryologist takes around 10 cells of the embryo, sends the sample to the genetic lab, and the embryos are checked to see if there are any abnormalities in the number of chromosomes. PGT-A doesn’t check for specific genetic diagnoses. PGT-M testing is done to evaluate the embryos for genetic disorders before implantation, and has been designed for individuals who know they are at an increased risk of having a child with a specific genetic disorder.
Embryoscope is another tool that can be used that allows the embryologist to see the embryos by microscope 24 hours continuously, so they can see their de development, they are monitored, and it helps to recognize and identify healthy embryos.
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The number of embryos a clinic may transfer is set by law in several countries. The IVF Abroad Patient’s Guide 2026 (IVF Media) lists a maximum of three embryos per transfer in Spain and two in Denmark and Turkey, with other countries leaving the decision to the clinic and the patient’s age.
I would recommend an immunology examination to check the antibodies and natural killer cells (NK). Also, hysteroscopy is a biopsy of the endometrium because you had a lot of tries and it doesn’t work. There have to be some issues that cause this.
There is a higher chance of pregnancy if 2 embryos are transferred, but also a higher chance of multiple pregnancies, which can cause a lot of additional risks. Therefore, the chances are not being doubled, if we compare the percentage of a success rate compared to the risks, the risks are a lot higher, and that’s why the doctors don’t recommend it.
It’s not some general recommendation, and it’s an individual thing. If a woman is 49 years old and she has only two embryos blastocysts or not of not high quality, it’s something to consider. This would be the only situation in which I would recommend doing a double embryo transfer, but in the other cases, I think it’s not the best option. However, there is no right time or the right age where we would recommend double embryo transfer because multiple pregnancies are a high risk for a woman’s body. It has a big impact at any age from the medical point of view.
Preeclampsia is a pathology, it’s high blood pressure, and it causes a lot of other complications for a mother and baby. Sometimes, it is necessary to do a preterm birth because of the bad condition of the woman, and sometimes we have to do an immediate C-section because of a woman’s high blood pressure. High pressure could cause the abruption of the placenta, and it’s a really dangerous situation during pregnancy.
During the whole 5 days of the development, we don’t take the embryos out of the Embryoscope or change the medium, that’s the biggest advantage of the Embryoscope or time-lapse in general. The embryos are monitored 24 hours a day, and we can watch them without the need to take them out and change the temperature, which could have an impact on their development. The culture is not changed.
If the Embryoscope is not used, the embryos need to be taken out and checked under the microscope and then put back.
It will be dissolved by the endometrium.
Yes, it is.
The endometrium has to be more than 7 millimetre high, we’ve known this for about 10 or 20 years, everything depends on the quality of the endometrium and its receptivity. It has to be higher than 7 millimetres for the optimal chance of success. Its quality is also very important, it should be a tri-laminar or triple line pattern otherwise, it’s just not going to work.
Poor quality endometrium can cause failure, even if the embryo is of the best quality embryo. For a successful pregnancy, we need high-quality embryos and optimally prepared endometrium. If there is some problem on the embryo’s side or the uterus’s side, especially on the endometrium, it will fail. When we do a whole IVF cycle and we do egg retrieval, and fertilization and then we wait for the fifth day, for the blastocyst, and when we see on the ultrasound that the endometrium is not optimally prepared, I always recommend freezing all the embryos, not to proceed with fresh embryo transfer. Then focus on the endometrium, prepare it better and follow with frozen embryo transfer in the next cycle.
It could be a problem, but I don’t think it’s only that reason, it could be a part of it though too.
We prefer to freeze embryos, not oocytes, and at our clinic, we freeze oocytes only during social freezing for women who don’t have a partner or don’t want to have a child yet but want to freeze their eggs for the future. In other cases, we recommend freezing the embryos, not oocytes. Every oocyte of good quality that is mature will be fertilized.
It’s very individual, and it’s about the condition of the embryo and how many embryos we have. If we have 10 embryos and only one is day 3 in a bad condition and the others developed, there is no need to use that embryo. However, if we only have 1 day 3 embryo and the development is not optimal, and if the embryo is not in a good condition, it’s best to do the transfer because we have no other possibility.
