Methods to improve frozen-thawed blastocyst transfer outcomes- the IVF laboratory perspective

Abstract

During the last few years, the number of frozen-thawed embryo transfer cycles (FET) significantly increased due to the universal application of more efficient cryopreservation techniques in the IVF laboratory and the improved survival rates of blastocyst stage embryos and the wide implementation of “freeze all” IVF cycles to prevent OHSS, or for preimplantation genetic testing for aneuploidy (PGT-A). Blastocyst cryopreservation allows single embryo transfers to reduce the rate of multiple pregnancies and improve perinatal outcomes. There is no consensus regarding the optimal laboratory protocol for blastocyst cryopreservation, and research is ongoing for its amelioration. This review summarizes different laboratory methods that may improve frozen-thawed blastocyst embryo transfer outcomes, alone or in combination. Some of the techniques relate to embryo survival; some of them work on endometrial receptivity.