Vitrification of embryos The vitrification of embryos consists in freezing the excess good quality embryos, from an own in-vitro fertilisation cycle or from a reception of oocyte process, to be used subsequently. This technique is useful both for couples who have not managed to achieve a pregnancy in the fresh cycle, and those who want a second gestation. To start a cryo-transfer cycle it is not necessary to go back and repeat ovarian stimulation. The treatment consists in an endometrial preparation through hormone replacement therapy (oestrogen patches or tablets and progesterone in vaginal suppositories). The embryos are usually thawed the same day as the transfer, which is carried out after confirming their survival and feasibility.