Dr Cinzia Caligara, gynaecologist at IVI Clinic Seville, explains why at IVI clinic doctors recommend single embryo transfer (SET) in Assisted Reproduction Treatment (ART).
The shift towards single embryo transfer (SET) in Assisted Reproduction Treatment (ART) reflects a commitment to improving outcomes for patients while minimizing risks. At IVI Clinic, fertility doctors advocate for SET as the gold standard for safer, more effective treatments. Dr Cinzia Caligara shared insights into why this approach is highly recommended and how it enhances the overall success and well-being of our patients. She discussed the benefits of SET and its role in modern fertility care.
An Elective SET involves transferring 1 carefully selected embryo from a group, ensuring a high chance of implantation while minimizing the risks associated with multiple pregnancies. This is distinct from cases where only one embryo is available, as the choice of embryo in the elective SET allows for the best quality to be selected.
Dr Caligara explained that one of the main reasons for preferring SET is to avoid the complications of twin pregnancies. While transferring 2 embryos may slightly increase pregnancy chances by about 5%, it drastically elevates the risk of twin pregnancies, which occur in 70% of such cases. Twin pregnancies carry a higher likelihood of premature birth, congenital malformations, and maternal complications such as hypertension, diabetes, and premature labour.
It’s crucial to remember that the main goal is not just pregnancy but ensuring the birth of a healthy baby with minimal risk to the mother. SET aligns with this objective, as cumulative success rates—achieved by transferring one embryo at a time—actually result in more healthy newborns over time compared to transferring multiple embryos simultaneously.
Dr Caligara also highlighted that advancements in embryo culture to the blastocyst stage (day 5) have significantly improved success rates for single embryo transfers. While twin pregnancies can still occur due to rare zygote splitting, the risk is minimal, at around 1.5%.
You might be interested in:
Elective single embryo transfer is a transfer of only one embryo when we can choose that embryo from a group of embryos. This is different when we have only one embryo, this is not elective single embryo transfer then.
Basically to avoid twin pregnancies. Nowadays, most of the clinics and also in our clinic we have very good pregnancy rates with single embryo transfer. Transferring two embryos will add around 5% higher chance of pregnancy with around 70% of the risk of twin pregnancy, and we know that the twin pregnancy has higher risk both for the babies and for the mothers. The main risk is premature labour and birth, with all the pathology associated, a higher risk of congenital malformations. For the mother, a higher risk of hypertension, premature labour, diabetes, Polyhydramnios, and the point is even if the risks of a twin pregnancy are assumable, the ultimate goal is to have a healthy baby, and a healthy mother and this is easily achieved with a single embryo transfer. We do not lose a significant amount of chances of pregnancy, so that’s why we recommend and we prefer transferring one embryo at a time. If we see the cumulative pregnancy rate so the total newborns after a cycle, we have more babies if we transfer one and then another one than if transfer two at a time.
The main is the risk is premature birth. The risk of premature birth is present even in a singleton pregnancy, this is like 1 out of 10 of the singleton pregnancies to be born before week 37. In twin pregnancies, the risk is 6 out of 10, and in triplets is 9 out of 10, and in higher-order, it’s 100%. The average time of delivery of twins is 36 weeks. If the baby is delivered before 37 weeks, there are stages of prematurity, it depends on the neurology unit care of the hospital where we are going to deliver but usually, the survival is at around 28 weeks with a high rate of complications and at about 32 weeks it’s a higher survival. The point is if patients want to have a twin pregnancy what I would suggest is to ask not only her obstetrician about the risks for twin pregnancy but also check with your paediatrician what is the advice that the paediatrician we’ll offer. Probably the obstetrician will be okay with a twin pregnancy, but for the neonatologists not, it will not be the same opinion, and the paediatrician and your neonatologists will push for a singleton pregnancy.
Nowadays, with the blastocyst stage embryo transfer in absolute numbers it increases by about 5% and why is it not double or higher than that? Probably, because there is a lot of immunological dialogue between the endometrium and embryos that with two embryos, it increases the chance that one is compatible and the other is not. Some studies have interestingly demonstrated that if we transfer 1 good quality embryo alone, we have a higher chance of pregnancy than if we transfer 1 good embryo with 1 accompanying embryo of not so good quality. It has usually, 5% higher percentage of pregnancy but with a higher risk of twin, and if we transfer one embryo, we end up with more newborns that if we transfer the two embryos at the same time.
Yes, it is possible to have twins after a single embryo transfer because of the phenomenon of the twinning of the zygote and those will be identical twins depending on how early the splitting occurs. They can have 2 placentae and 2 amniotic sacs, so just have shared the placenta with 2 amniotic sacs, or share the placenta and share amniotic sacs or be conjoined twins. The twins that share a placenta have a higher risk than the twins that have each own placenta and amniotic sac and so on. This can happen either with one embryo transfer, the incidence is low is about 1 in every 80 pregnancies, that’s about 1.5%, but it can happen also if we transfer 2 embryos and one of them can have these phenomena of twinning, so we end up with a triplet pregnancy.
Well, mainly to day – 5 embryos because we know that around half of the day-3 embryos don’t evolve to the blastocyst stage. So we’re speaking about the transfer.
It happens very early after implantation, and it depends on the moment the embryo will divide completely and this will lead to monozygotic dichorionic diamniotic twinings, so identical twins from one embryo, one egg and one sperm with 2 placenta and 2 amniotic sacs or which is more common, only 1 placenta and 2 amniotic sacs or one placenta and one amniotic sac or the conjoined twins.
I’m not an embryologist, but I’m aware that with the new method of vitrification, it’s a very safe procedure because the problem that occurred with slow freezing that was the formation of ice meals is not present, so the risk of not surviving after vitrification is less than 5%, but I’m not an embryologist, so I don’t know if these answers the question.
We now, at IVI have a protocol that has been developed after excessive research that if the absorption of vaginal progesterone doesn’t reach a level of progesterone above 8 picograms per millilitres in blood, we supplement with subcutaneous progesterone, and this supplies the lack of progesterone. If the level of progesterone is above that level, it is not necessary to use injected progesterone unless the patient wants to because of the comfort of not using vaginal pessaries. In Spain we do not have oral progesterone commercialized, and now we have the subcutaneous progesterone, and we do not have a commercial form or intramuscular progesterone is a pharmaceutical firm that is made especially for the patient, it’s not commercially available.
Yes, there is no contraindication.
That is a normal level, but when we are looking for a pregnancy, we do prefer to have the levels of TSH below 2.5. If you were a patient of mine, I would give you some medication to lower the level of TSH so that the level is 2.5. Even if 3.24 is a normal level and if you are not looking for a pregnancy, an endocrinologist will not give you treatment until the TSH of 11 or more.
I would suggest having a consultation with your gynaecologist to see your ovarian function. At 44, you can be starting the perimenopausal period, which at 44 is an early one but not an abnormal one. I would suggest having a consultation with your gynaecologist to assess your ovarian function.
Do you test only on the day of the transfer? As I’ve mentioned, in our clinic (IVI Seville) we have a protocol of testing the progesterone at the day of the transfer and check the levels. I think more clinics are doing that, more clinicians are doing such testing, but it is like a recent addition to controlling the cycle. So I think the dosage is quite high to have a good level of progesterone.
We test routinely on the day of the transfer, and if it is okay, we do not test anymore. If it is very low, we supplement with the subcutaneous progesterone in selected cases sometimes we test again after 2-3 days to make sure that the supplementation is working and we have adequate levels of progesterone. In egg donation, we start with 400 milligrams twice a day
No, it’s safer to have a single embryo transfer. I mean chromosomally euploid embryos will have a higher implantation rate. The aneuploidy is the most common cause of recurrent miscarriage, we need to minimize the impact of the immunological issues, so the recommendation in recurrent miscarriages is to avoid twins, to have a single embryo transfer. Because having twins is a risk factor for miscarriage and a patient with recurrent miscarriage doesn’t want to have another miscarriage.
The scientific evidence up to today is that there is no more risk of miscarriage with COVID infection.
Yes, it’s part of a diagnostic exam to tests patients with recurrent abortion.
There are pros and cons. One of the pros is to be sure that the endometrium will respond properly, then we can check the progesterone in the mock cycle also and be sure if we need to supplement with progesterone or not. We also can do some studies of the endometrium, of the implantation windows and of the bacterial media of the uterus and the amount of lactobacillus. We do not routinely do a mock cycle, it depends on the patient, we personalize upon the history of the patient. The con is that you are adding one month to the treatment.
That will depend on the lab at your IVF centre. I can speak how it works in our clinic, we are completely sure that our lab is a safe place for the embryos and we do not perform day -3 embryo transfers, we go to day-5 in all the patients.
