Michelle Emblenton, a biochemist at inviTRA, tells us about how the number of embryos to be transferred is decided:
When deciding the number of embryos that are going to be transferred, as well as looking at the quality of the embryos, we also take into consideration factors such as the maternal age, the origin of the egg cells (whether they are from own egg cells or whether they have been donated), the receptivity of the endometrium and the actual reasons for the infertility itself in the first place are also looked at. Any previous cycle failures, for example due to implantation failures, and also the stage at which the embryo is transferred (is it transferred at day two to three of development or at the blastocyst stage at day five of embryo development).
Embryos are classified from grade A to D, with A being the best quality embryos and D being the poorest quality embryos.
We do have an article on this and in the main article here we have a link to this article where you can find exactly what it is in the embryo that makes them a top quality grade A embryo or a poorer quality grade D embryo.
All of the factors I've mentioned previously will be considered when making the final decision of how many embryos to transfer, so let's look at two possible circumstances.
The first circumstance could be a young patient, perhaps 28 years old, with really good quality (A quality) embryos. She's not had any previous IVF failures and not had any miscarriages. In this case, it is highly likely that your specialist will choose to transfer only one embryo because the prognosis is very very good.
Conversely, in for example an older patient, perhaps 38 years old, with maybe only three or four quality C grade or D grade embryos, the specialist may choose to transfer two, possibly even three embryos, to increase the chances of the treatment being a success.
As I've stated, these are always decisions made on a case-to-case basis. Indeed, many countries have laws governing the number of embryos that can be transferred, and there is a general consensus in this, as we have discussed, that the younger patient with good quality embryos the maximum is one or two, with a maximum of three being transferred in older patients with poor quality embryos. Usually, if donated eggs have been used, the maximum number of embryos permitted to be transferred is two. Again, as with all the assisted reproduction treatments, laws vary from country to country and state to state. For example, in Spain and the UK they are tightly regulated by the governing bodies, whereas in the United States they are more guidelines than laws.
