Evidence-based ET: What is the best protocol for cryopreserving IVF-derived bovine embryos?

Evidence-based ET: What is the best protocol for cryopreserving IVF-derived bovine embryos?

John F. Hasler

Note: The title of this column was suggested by our AETA board of directors

There has been concern regarding the best way to cryopreserve bovine IVF-derived embryos ever since commercial in vitro embryo production (IVP) started in the early 1990s. Donors in the early days were primarily infertile, problem donors, and annual IVP embryo production in the United States was limited to a few thousand embryos, at most. Production of IVP embryos has increased substantially in recent years, and in 2013, it was reported that 48,112 embryos were produced from OPU collections compared with 301,671 in vivo embryos collected from superovulated cattle. Thus, 13.8% of the total embryos produced were from IVF procedures and 55% of them were reported to have been frozen. It is anticipated that reported IVP production will be substantially higher in 2014. Understandably, the companies providing IVF services are reluctant to share details of their cryopreservation services. However, because fresh IVP embryos are often shipped overnight to ET practitioners/donor owners for transfer on-farm, embryo numbers sometimes exceed the number of available recipients. Consequently, not infrequently, practitioners are faced with cryopreserving leftover IVP embryos. Even today, however, there does not seem to be any widely agreed upon, best protocol for cryopreserving IVP embryos. In the last few years it has been publically reported that IVP embryos have been commercially cryopreserved by vitrification and slow freezing with both ethylene glycol (EG) and glycerol used as the cryoprotectants.

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Evidence-based ET: What is the best synchrony between IVP embryos and recipients?

Categories: Evidence-Based ET
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Published on: September 10, 2014

Evidence-based ET

John F. Hasler

Note: I have been using subjects suggested by our board of directors for this column for the past two years.  I would be happy to attempt covering any subjects that the membership might suggest. Let me hear from you!

What is the best synchrony between IVP embryos and recipients?

There is a great deal of evidence that synchrony between the age of in vivo-derived embryos and the day of the estrous cycle in recipients at the time of transfer is affected very little, if at all, when synchrony is within the three day period of 0, plus one or minus one day (zero, meaning day of estrus and age of embryo are the same).  Consequently, the pregnancy rate is not affected when day 7 embryos are transferred into day 6, 7, or 8 recipients.  This holds true for both fresh and frozen in vivo-derived embryos (Hasler, 2001).

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