Received September 13, 2001
Accepted October 09, 2001

The transfer of embryos at the blastocyst stage has been increasingly employed after the introduction of co-cultures and sequential media, and excess blastocysts are commonly frozen. ln the present study, three blastocysts were frozen using the slow protocol with glycerol as cryoprotector. Before freezing, the embryos were passed through a 5% glycerol solution followed by 9% glycerol plus 0.2 M saccharose. The embryos were rapidly thawed and transferred to a 5% glycerol plus 0. 1M saccharose solution, and then passed through a solution containing only 0.1M saccharose. After 2h of incubation in culture medium the embryos were transferred to the patient. Pregnancy was confirmed by the presence of a heart beat 6weeks after transfer. Therefore, embryo freezing at the blastocyst stage is not an obstacle to prolonged culture.