CRYOPRESERVATION OF HUMAN EMBRYOS AND OOCYTES

Human embryo cryopreservation is now a fully established adjunct to as sisted reproduction, with thawed embryos implanting at a rate approach ing that of fresh embryos. As with fresh embryos, the quality of froze n-thawed embryos is affected by patient age at the time of oocyte retr ieval, and by culture conditions. Ovarian stimulation incorporating go nadotropin-releasing hormone analogs does not appear to be detrimental to cryopreservation success, and natural or artificial thaw cycles se em equally effective. Successful cryopreservation seems feasible for o ne- to eight-cell embryos and blastocysts using a variety of protocols . Selection criteria for embryos to be frozen can vary, and embryo qua lity has the most significant impact on post-cryopreservation viabilit y. Unfertilized oocyte cryopreservation is coming closer to routine cl inical application.