Cryopreservation of human embryos.

This chapter describes general cryobiological principles and the different methods for cryopreservation of supernumerary human embryos obtained after several procedures for medically assisted procreation. Different factors that influence the performance of freezing and thawing of human embryos are reviewed: the data from international and national surveys of results, the cryopreservation procedures, the stages of embryonic development, the morphological appearance of the cryopreserved embryos, the numbers of embryos transferred, the storage times of embryos in liquid nitrogen, the ovarian stimulation protocols in the IVF cycle and the replacement cycles of cryopreserved embryos. Cryopreservation of embryos circumvents the difficult problem of synchrony between the ovarian cycles of donor and acceptor patients in an oocyte donation programme.