Vitrification Update

Since March of 2007, PFC has been vitrifying embryos. We have now completed over 600 warming cycles, utilizing those embryos. Vitrification is proving to be a very reliable technology to preserve any unused embryos that remain after a fresh transfer. We continue to adjust our technique and thus increase the successful results of vitrification. Last year, we introduced a modification to the procedure that allows us to remove the fluid from the cavity in a blastocyst before we begin vitrifying. As with any freezing procedure, cell water must be substantially removed and replaced with cryoprotectants to avoid ice formation in the cells. Five and 6 day old embryos, or blastocysts, can have a large fluid filled cavity that slows dehydration and passage of cryoprotectant into the cells. Since vitrification is an ultra-rapid freezing procedure, any delays caused by the fluid in the cavity may affect the ability of the embryo to survive the procedure. By making a small breach between two of the outer cells in the embryo, we are now allowing the cavity to collapse prior to beginning the vitrification procedure. This artificial collapsing has further enhanced results. We are seeing implantation rates with warmed embryos that are very similar to those achieved with fresh embryos.

Overall, from 636 warming cycles, we have achieved 284 clinical pregnancies (45%) in all age groups combined. In younger patients (maternal age under 35), there were 103 successful clinical pregnancies from 190 transfers (54%) with an average of just 1.7 embryos transferred. This pregnancy rate drops to 42% (41/97) in 36-37-year-old patients with an average transfer of 1.8 embryos. In the 38-40 age group there were 31 pregnancies achieved successful from 79 transfers (39%). For patients over age 40, 8 of the 23 transfers were successful (35%). In the donated oocytes group, 101 pregnancies resulted from 247 transfers (41% with an average of 1.7 embryos transferred). For patients that had their embryos artificially collapsed, the results were better. However, since this is a new technique, the number of cycles is small.

Overall, we are very pleased with the outcomes achieved with vitrified embryos. We are optimistic that results will continue to improve. The table above shows results for all cycles completed since the beginning of the vitrification program. As our experience grows, so do our success rates. Reviewing cycles of patients that had embryos warmed and transferred from just this year (Jan-Oct 2010), we see that the outcomes are exceptionally good, particularly for patients whose embryos were collapsed prior to vitrification.

At PFC we are continuing to vitrify all embryos by day 5 or 6 after oocyte retrieval if they are good or reasonable quality blastocysts. We now routinely collapse any blastocyst with an expanding cavity. These procedures have worked well. Consequently, it has become necessary to reduce the number of embryos being transferred to avoid generating too many multiple pregnancies. Our goal is to achieve a healthy singleton pregnancy in all patients; vitrification has allowed us to reduce the incidence of multiples by transferring just a single embryo most of the time. For our 2009 fresh cycles, in patients under 35, 40% of the time we transferred just one embryo, and in patients using donor oocytes 60% of the transfers were a single embryo. Vitrification has proved to be so successful that many patients have elected for a fresh single embryo transfer; virtually eliminating their risk of twins and knowing that their frozen embryos will be available should they be needed.

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