I-5: Cancellation of Fresh Embryo Transfer: A Future Perspective

Controlled ovarian hyperstimulation (COH) affects adversely implantation following in vitro fertilization and embryo transfer. COH with gonadotropins alters endometrial receptivity and luteal function. In addition periovulatory endometrial characteristics in stimulated cycles are considerably different compared with the natural cycles, and periovulatory secretory transformation is consistently advanced. It has become apparent that if secretory endometrial advancement in the early luteal phase is more than three days, implantation does not occur in human. An embryo-endometrium asynchrony in COH cycles impairs implantation. The window of implantation closes earlier in COH cycles. It has been suggested that the asynchrony problem in fresh cycles can be solved by cryopreservation af all embryos and transferring them subsequently in optimal conditions. The endometrial development in frozen-thawed cycles can be controled more precisely than in the cycle of COH with gonadotropins, therefore there is less asynchrony between endometrium and embryos in FET cycles and such patients would have an increased chance of pregnancy. Vitrification is ultra-rapid method of cryopreservation whereby the embryo is transitioned from 37 ºC to -196ºC in < 1 second., resulting in extremely fast rates of cooling (> 50,000ºC /min). High concentrations of cryoprotectants together with rapid cooling rates are essential to cryopreserve embryos in a vitrified, glass-like state. Vitrification has several advantages. The main benefits include the lack of ice crystal formation, made possible through increased speed of temperature conduction, reducing associated chilling injuries. A practical advantage is that the speed of process and there is no need for expensive equipments. Vitrification is assotiated with less celluler trauma than slow freezing and the cryosurvival rate with vitrification is ~95%. Therefore, vitrification is considered as the method of choice for human embryo cryopreservation. Through a long standing experience with the vitrification method and a higher pregnancy rate in frozen/thawed cycles than the fresh embryo transfer, it can be recommended to vitrify all the zygotes or all the embryos and replaced in a programmed cycles for the benefit of the patients.