Blastocyst Vitrification: The First 2 Years
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In 2007, PFC took the bold step of changing the way we freeze embryos. Traditionally, embryos are frozen using a “slow-freeze” protocol where they are exposed to weak concentrations of cryoprotectants before being cooled slowly (-0.3 °C/min) for 2-3 hours. This system has worked well over the years, but recent advances in an ultra-rapid freezing technology showed great promise. PFC began looking at a technology called vitrification in 2006. After seeing wonderful results from in-house trials we were able to phase vitrification into our practice in March of 2007. By June, we had stopped slowfreezing completely. In late 2008, after our 200th thawing cycle with vitrified embryos, we examined the data.
From our first 2 years of thaws, we recovered 94% (423/448) of embryos vitrified, and 94% (397/423) of these were alive when the thawing process was completed. The total number viable was 88% (397/44 8). These numbers compare well to those reported in the scientific literature, but we continue to improve the process and strive for even better results. Vitrification uses tiny straws called “cryotips” to house the embryos during the process, and uses higher concentrations of cryoprotectants than slowfreezing. These details make the procedure technically challenging, which may sometimes result in the loss of an embryo. The tiny straws can crack or break due to the extreme physical force that they endure during freezing and thawing. If this happens, the embryo in the straw cannot be recovered. This lack of recovery or survival is a complication of any freezing procedure. We continue to go to great lengths to minimize these losses, some of which are unavoidable.
We have completed 202 thawing cycles to date (A thawing cycle refers to a treatment cycle wherein a patient returns to use vitrified embryos and we thaw and transfer 1 or more to her uterus at the same time). Ninety-seven of these 202 cycles (48%) resulted in an established clinical pregnancy. The average number of embryos transferred per cycle was 1.9 and the implantation rate (embryos implanting out of embryos transferred) was 31%.
The vitrification procedure and materials continue to evolve. Irvine Scientific, the company that manufactures the cryotips, continues to improve their product. They are working extremely hard to eliminate defects that may lead to straw failure during cooling and thawing. At the same time, PFC continues to evaluate new ways to improve embryo survival and implantation rates. This year, we are investigating a process which artificially collapses blastocysts prior to vitrification. We will also be investigating the use of assisted hatching with thawed embryos. Be sure to watch these pages for exciting updates in the months to come.
Tags: Embryo Freezing
