This is a common question we have from patients. The answer depends on the lab and on the success rate each IVF lab has. It does not depend on the PGS or PGTA procedure. Actually the embryos that need biopsies are not all on the same developmental stage. Some are excellent, some are medium and some are not good looking which is indicative of their development. This question can be answered based on morphology and development of the embryos. Most of the papers and research show you can get the same results and pregnancy rates when you transfer one or two embryos. However this depends on the development of each embryo. So the chromosomes you are testing are only part of the journey of having pregnancy; it’s not the whole part. The embryos should also have a good development and indications that it is developing in a nice way so it can have a chance of implantation.
We always recommend transferring one embryo at a time, and the reason is very simple. You want to check that the procedure has been done correctly and there is no misdiagnosis.
First of all, if you have twins, you are multiplying the risk of women being misdiagnosed by two. Secondly, with invasive tests like chorionic villus sampling or amniocentesis, you have a higher risk of miscarriage if you have two distinct chambers with two distinct fetuses instead of one. Thirdly, if one of the two individuals is chromosomally abnormal and the couple decides to terminate the pregnancy even in the hands of the best obstetricians, the selective abortion is also deleterious to the remaining chamber carrying a normal, healthy individual, 30-40% of the time.
So there is no need to do a double transfer. Also, if you have a receptive uterus in that month, your chance of transferring two embryos and having twins is very high. If in that specific month your uterus is not receptive, you are losing both embryos that are chromosomally normal because they do not implant because of the uterus. So statistically, it is a mistake to transfer more than one embryo.
We would usually recommend transferring one embryo after PGS. It’s true that with PGS, we are not going to fix any of the problems that the embryo may have, but by discarding those that are genetically abnormal, we are going to increase the live birth because of the risk of having a miscarriage is going to be much lower. It’s an extra way of confirming that the embryo is not just pretty but is also genetically normal, and the implantation rates and the ongoing pregnancy rate is going to be much higher.
We think that regardless of the patient’s age when we have confirmed that the embryo is genetically normal, the single embryo transfer is absolutely recommended.
