Identical twins are something that can happen; it’s not very common, but it could occur. This fact has nothing to do with the number of embryos that we transfer. It’s a process that is basically decided by the embryo itself. We don’t know the reasons, but we have had patients in whom we carried out a single embryo transfer, and they ended up with a twin pregnancy or, even more rarely, a triplet pregnancy because the embryo may divide itself into 2 or 3. According to statistics, this happens approximately twice a year, and we don’t have a specific profile of patients in whom this is more common.
Good questions. Of course it will depend on the number of embryos that we are gonna transfer. Routinely, nowadays the trend is that women under the age 40, we would only transfer our advice to transfer a single embryo transfer. We all know that one of the things classically heard from IVF is that you get multiple pregnancies. You get twins, triplets is very rare nowadays because by the law of this land, we are only allowed to transfer a maximum of 2 embryos in women up to the age of 40. That has drastically reduced the multiple pregnancies rate. Having twins in IVF should be an exception rather than a rule and we should all very concisely and responsibly advise our patients to transfer a single embryo. It is important for me to say that at this point that the pressure of choosing the right embryo, should be on the embryologist. Not this hazard rule “let’s put more to get her pregnant”. NO! We should have the ability with the current technology to select the right embryo with the highest implantation potential. There are several tools within the lab that we now have including Artificial Intelligence that tells us which embryo should be the best embryo to put back. My opinion is always: one at a time unless the patients had multiple cycles without any success or implantation failure, then they can consider putting two embryos back but they should be mindful that the risk of twin pregnancy is there. You can always have a monozygotic twin which means one embryo splitting into two, so even if you put one embryo it can split in two and result in twin pregnancy. The chances of this happening is very very slim. It is less than 2-3% but that risk is always there. The risk is much smaller than putting two embryos back.
All embryos have the capacity to split into twins. If a single embryo splits into two and they both implant, it will lead to a monozygotic (identical) twin pregnancy. This occurs in approximately 1% of treatment cycles.
If two different embryos are transferred and they both implant, the pregnancy will be a dizygotic (non-identical) twin pregnancy. It is also possible for one or both of two transferred embryos to split into twins, leading to higher-order multiple pregnancy (triplets or more). This is rare, however it can still occur.
