Cryopreservation of human oocytes and embryos

Abstract

With the advent of assisted reproductive technology, controled ovarian hyperstimulation (COH) is usually carried out to stimulate the growth of multiple follicles and produce multiple oocytes. Accordingly, multiple embryos are transferred to the uterus to increase the chances of success. However, multiple embryos can also increase the likelihood of multiple pregnancies, which are accompanied by a whole series of complications affecting both mother and child. There has been a trend toward transferring fewer embryos during the last decade. According to Center for Disease Control and Prevention (CDC), the average number of embryos transferred to women under 35 has dropped from 4.0 in 1995 to 2.8 in 2001 in the United States (N Engl J Med 350:1639-1645, 2004). In Europe, IVF centers in many countries have reduced the number of replaced embryos to two or even one (Ann N Y Acad Sci 1034:110-116, 2004). It is, therefore, very important to have a reliable technique to effectively cryopreserve the supernumerary embryos after transfer. The first pregnancy following the transfer of a frozen-thawed human embryo was reported by Trounson et al. in 1983 (Nature 305:707-709, 1983). Since then, embryo cryopreservation has become a very important part of the clinical use of in vitro fertilization. To date, human embryos have been successfully cryopreserved at the pronuclear, cleavage, and blastocyst stages of development. Moreover, recent advances in cryopreservation techniques have expanded the female fertility preservation from embryo to oocyte and ovarian tissue. © Springer Science+Business Media, LLC 2010.