The number of embryos that manage to enter the endometrium will depend mainly on how many embryos have been transferred, their quality and the receptivity of the endometrium.
Thus, the fact that two embryos are transferred does not necessarily mean that a twin pregnancy will occur. It is possible that both will implant, but it is also possible that only one or even none of them will implant.
If the quality of the embryos is good (type A or B embryos), the probability of implantation will be higher. In these cases it is recommended to transfer only one embryo to avoid multiple pregnancies.