In many IVF cases, more than one good embryo is obtained. Having many good embryos available allows fertility specialists to grade them and choose the best ones for transfer. But this also causes a common dilemma – how many embryos should be transferred?
Interested? Read what Dr Jessica García
[Fertility Specialist at Clinica Tambre
] says about Single embryo vs. multiple embryos for transfer. Best practices and recommendations
during this #IVFWEBINARS.
An embryo transfer – the background
An embryo transfer is the last part of fertility treatment. The last – but also the most important one. Using ultrasound for accuracy, the doctor will pass a catheter through the woman’s cervix and into the womb. From there, the embryos are passed through the tube and placed into the endometrium. Dr Jessica García starts her presentation by explaining that an embryo transfer is quite a simple procedure that does not require anaesthesia. There are three types of embryo transfers: a single transfer or elective single transfer (when there is more than one embryo of good quality), a double transfer and multiple transfers (when 3 or more embryos are transferred). Dr Garcia admits that in Spain, there is usually the choice between options 1 and 2. However, there are still countries that transfer more than 3 embryos.
Dr Garcia sheds some light on the history of embryo transfers. In the late 1970s, as there was no vitrification method yet, doctors were forced to transfer all the good embryos they had retrieved. It meant transferring 3-5 embryos at once. It resulted in lots of twin/multiple pregnancies through IVF. In the 1980s, the lab culture of embryos started to prolong, and embryo transfers slowly moved from day 1 to day 3. When the incidence of multiple gestations increased to 15-30%, entailing a risk of pregnancy complications, fertility specialists started looking for new technologies to improve embryo selection. The late 1990s brought the first attempts at a single embryo transfer.
Improving embryo selection with long culture
Dr García says there are almost 9 million babies born through IVF in the world today. This impressive number was achieved partially thanks to new technologies that have significantly improved the process of embryo selection. One of them is the so-called long culture. Culture is used to recreate the environment within the fallopian tube and uterus so that embryos can grow just as they do in the human body. Embryology labs have become capable of culturing embryos safely for longer periods of time – up to the stage of a blastocyst (day 5). Blastocysts, being embryos with the greatest potential, have more psychological synchronisation with the endometrium. They are the ones with activated genome and – what is more – they have a lower rate of early miscarriage when being transferred. Dr Garcia admits that only the hardest and strongest embryos can advance to the blastocyst stage. Thus, the latter is also the best stage to conduct genetic testing on embryos.
Embryo vitrification as the solution
According to Dr Garcia, nowadays, embryos can be successfully frozen and thawed better than ever. Thanks to the vitrification method, good-quality embryos, that are not immediately transferred to the patient, are placed in cryostorage. It means that they are frozen and stored until they are needed for the later transfer – without decreasing their quality. Compared with the times when only fresh embryos could be transferred, that is a really significant improvement.
Time-lapse and a higher rate of blastocysts
A new generation of time-lapse incubators enables embryologists to culture embryos from day 1 till the blastocyst stage – without the need to remove them. These incubators help to maintain an uninterrupted cultural environment, including constant factors such as temperature, oxygen and light exposure. Additionally, there is a possibility of real-time image recording and embryo development monitoring. All of this help to select the best embryos to transfer, as well as decide which of them should be transferred first. Dr Garcia also mentions one very important issue – the rate of blastocysts is noticeably higher when using time-lapse incubators. And the advantages of blastocyst transfers are more than clear – it has already been proved in the previous paragraphs.
PGS for chromosomally normal embryos
Of all new technologies improving embryo selection, pre-implantation genetic screening (PGS) is of the highest importance. In this procedure, cells taken from developing embryos during a biopsy are sent to the lab, where they are assessed in terms of chromosomal euploidy. PGS helps to select chromosomally healthy embryos and, as a result, increases the chances of a healthy baby. Thanks to this technology, it is possible to reduce the risk of miscarriage and increase the chance of pregnancy per transfer. Additionally, doctors can reduce the duration of treatments and the number of cycles to achieve pregnancy.
However, Dr Garcia stresses that PGS is not indicated for everyone. It should be considered mainly by women over 37 years old, patients who suffered from two or more miscarriages or those who previously had a genetically abnormal pregnancy. It is also a good idea for people who underwent multiple IVF cycles with no successful outcomes.
Single embryo transfer vs. multiple embryos transfer results
Despite the use of the most up-to-date technologies designed to improve the embryo selection process, some patients still believe that the best way to increase the chances of live birth is by multiple embryo transfer. Dr García clearly highlights that multiple embryos very often mean a higher risk of multiple pregnancies. Even if you transfer just one embryo, there is still a 1% chance of it splitting into identical twins. So, when you decide to transfer two embryos, bear in mind that the possibility of twins or even triplets is quite real.
Dr Garcia states that the chances of pregnancy by either a single or a double embryo transfer are more or less the same. According to the Spanish Fertility Society (SEF) data from 2017, the pregnancy rate in case of a single embryo transfer (SET) was 53%, while in the case of a double embryo transfer (DET) – 56%. However, taking into account the possibility of a twin pregnancy, the difference is much more significant. In the case of SET, it is only 1.3%, but with DET – it is 31%. When we realise that each twin pregnancy entails much more risks and complications, this last comparison takes on a completely new meaning.
Twin pregnancy – the facts
Dr Garcia says that patients are not willing to acknowledge the fact that a twin pregnancy poses some real threat. On the contrary, they seem to treat it as a reward after their long and complicated fertility treatment. But one has to have a realistic overview of the situation to be able to make conscious decisions. The truth is that all the possible pregnancy risks are increased in case of double pregnancies. Firstly, and most importantly, the miscarriage rate is much higher in the case of the latter. Additionally, twins are not always born healthy and they are at risk of lower birth weight and prematurity, including all related complications. Twin pregnancies are also less beneficial for mothers. The women may suffer from pregnancy-induced hypertension, gestational diabetes and pregnancy bleeding. They are in the need of a caesarean section much more often, too.
In conclusion, Dr Garcia points to a few factors that should be considered when deciding between a single embryo transfer and a multiple embryo transfer. The most important is the cause of infertility – every patient’s case is different, and that is why the treatment plan always has to be individualised. Another factor is maternal age – here, the older the mother, the higher the risk of pregnancy-related complications. One also must take the patient’s medical conditions into account. Diseases, such as diabetes or high blood pressure, can only get worse in the case of multiple pregnancies. Finally, the possibilities of implantation can differ depending on the embryo quality. Transfers during the blastocyst stage generally give more possibilities of a pregnancy – it is a meaningful argument for single transfers and – at the same time – against multiple transfers. The quality of embryos is higher in egg donation and IVF treatment with PGS as well.
According to Dr García, discussing one’s own medical case with the doctor is crucial before deciding on the type of embryo transfer. Additionally, using all the described new technologies for embryo selection is advisable in order to improve pregnancy rates – without bearing unnecessary risks.
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