ABSTRACT
Among various high-rate cooling approaches used for vitrification of mammalian oocytes and embryos (discussed in detail in Chapter 2) two techniques have obtained relatively wide acceptance among embryologists: the Cryotop with extensive and rapidly growing application in the human field, and the open pulled straw (OPS) in animal reproductive biology. Although there is considerable overlap, with the first baby born after oocyte vitrification using OPS being reported, followed by high pregnancy rates being achieved recently after OPS use,1,2 and excellent results also being achieved with the Cryotop in animal reproduction,3,4 the field is more or less evenly distributed. The reasons are partially understandable, as domestic animal embryologists prefer to work with straws, and the more robust and simpler OPS also permits a kind of semi-direct transfer after warming,5
an approach that is not only very simple and practical, but also has not been found to compromise pregnancy and calving rates at all in cattle after transfer of in vitro produced or somatic cell cloned, zona intact or zona free embryos. This fact may provide considerable benefits for on-farm applications (see below). On the other hand, the beauty of the delicate approach of Cryotop, and even more the extremely convincing, and burgeoning statistics based on blastocyst cryopreservation (and
an increasing number of successful oocyte vitrification) results achieved in the world’s largest human IVF clinic are particularly attractive to human embryologists, and motivate them to attempt to replicate the published achievements. This distribution of applications seems to be established, and may remain for some years to come, although very few convincing statistics show the superiority of either of the two methods for any given purpose, provided the technique is applied strictly according to the established guidelines.
