The greater the number of embryos transferred, the higher the chances for at least one of them to implant, thereby achieving the ultimate goal of IVF: a pregnancy. Nevertheless, by doing it, the likelihood of getting pregnant with twins increases too, which would entail a higher number of risks than a singleton pregnancy.
To sum up, except under special circumstances, specialists do bet on elective single embryo transfers (eSET), which consists in selecting the embryo with the best quality for the chances of implantation to be increases without the need for a multiple embryo transfer.