Should We Transfer One or Two Embryos?
By Francis Polansky, M.D.
Whether created through intercourse, artificial insemination, or In Vitro Fertilization, most human embryos do not have the potential to hatch out and implant. Transferring (putting inside the uterus) more than one embryo may increase the likelihood that at least one embryo will implant.
In the US, there is no law that would limit the number of embryos to transfer, but at Bay IVF, we follow the recommendation of the American Society for Reproductive Medicine that most patients should transfer only one or two embryos.
There is no “crowding” effect inside the uterus. If you decide to transfer two embryos, the probability of live birth will be higher than if only one embryo is transferred. But if you do transfer two embryos and conceive, your treatment may result in a twin pregnancy.
The likelihood of a single transferred embryo resulting in a set of identical twins is approximately the same as in pregnancies conceived without IVF: about 1 in 250.
It is well known that a singleton pregnancy carries the lowest risk to the mother and newborn. Therefore, the delivery of a full-term, healthy singleton is considered the ideal outcome after the use of assisted reproductive technology treatments.
The number of embryos to be transferred is usually finalized during the embryo transfer visit to our Clinic. At that time, the number of embryos available for transfer and their quality assessment is known, and it is then possible to estimate the probability of a successful outcome with one or two embryos transferred. You would also know the approximate “risk” of a twin pregnancy if you decide to transfer two embryos.
The availability of highly reliable embryo vitrification has resulted in many patients choosing to only transfer one embryo at a time.
As you are deciding how many embryos to transfer, we will always provide guidance, but you will have the final say in whether to transfer one or two embryos.