12 - Cryopreservation of blastocysts

Summary

Cryopreservation techniques for blastocysts are required to preserve surplus blastocysts. Cryopreservation of the blastocyst was mainly carried out with a slow-freezing technique using programmed freezers. As a typical container for embryos, a cryostraw, includes both liquid (cryoprotectant) and solids, a slow change in temperature is needed to preserve cell structure. The vitrification method developed for mammals has recently been applied to human embryos. The chapter outlines a vitrification procedure for cryopreservation of blastocysts (Cryotop method). The cryopreservation of surplus blastocysts is beneficial, especially for day 6 blastocysts. When cryopreserved and thawed blastocysts are transferred into the uterus, two methods of endometrial preparation for transfer are available. One is transferring to the endometrium in the natural menstrual cycle and the other is to an endometrium prepared by hormone replacement. For patients who have a chromosomal abnormality, preimplantation genetic diagnosis (PGD) is applied for in order to choose normal embryos.