Frozen embryo transfer (FET) involves the introduction of one or more embryos into the uterus through the cervix. It is the culmination of an in vitro fertilisation technique. Transfer of embryos can be carried out with embryos from the in vitro fertilisation process or with embryos from a previous cycle that have been frozen for preservation. In the case of frozen embryos, to carry out the procedure the woman's uterus is first prepared, the embryos are brought to a physiological temperature (37°) and then transferred to the uterus. The transfer is done under ultrasound control to identify the ideal place to deposit the embryos. In recent times, a method of embryonic selection called embryoscopy has been put into practice, which allows the embryo to be controlled from the time of fertilization to the transfer to the uterus.