As both CRSC and VS have been more commonly used around
the world, the debate continues about which (or, if either) technique is superior for oocyte cryopreservation [55–58]. Recent systematic reviews in human oocyte cryopreservation comparing
either slow cooling methods or VS techniques found some evidence
that oocyte recovery, fertilization, and embryo development were
higher in the VS groups [31, 51, 59–61]. Due to different requirements in operator skills, process times, equipment availability, and
species-specific factors in oocyte biology, no single cryopreservation method is likely to be suitable in all situations, for all species or
for all developmental stages of oocytes. Many ancillary factors such
as oocyte quality and selection, hormonal stimulation regime, and
in vitro manipulation conditions can impact on cryopreservation
outcomes [6, 50, 62]. Even if VS is superior for oocyte cryopreservation, further studies on the fundamental biophysics of cryogenic
exposure could optimize both CRSC and VS protocols. As far as
can be assessed from current information, oocyte cryopreservation
does not impact in a negative way on birth abnormalities
[48, 50]. Oocyte cryopreservation has moved away from assignment as an experimental procedure, towards recognition of the true
value of this powerful technique with far-reaching potential in
reproductive technologies. As we approach the 2020’s, there is a
highly significant switch to VS for those centres performing oocyte
cryopreservation, such that, for example, in the UK and Scandinavia, none are now using CRSC (Fuller, Keros personal communication 2019). Therefore in this chapter, we shall concentrate on
providing details of the VS method. However still some scientists
are interested in details and principles of slow cooling, especially for
animal oocyte cryobanking. Thus we also present a robust method
and protocol details for murine oocyte CRSC [2]. Detailed explanation of the Cryotop
®
—Open System method (Kitazato Biopharma, Shizuoka, Japan)—successfully applied worldwide for
human oocyte VS can be found on the Kitazato company’s homepage (https://www.kitazato-dibimed.com/wp-content/uploads/
CRYOTOP_SAFETYKIT_A5_2019_LOW.pdf).
Two methods of oocyte cryopreservation are described below,
with the necessary technical details to introduce these into a standard laboratory setting and which have been developed over several
years for murine oocytes. One method is for slow controlled rate
cooling, and the other is a VS method. They can yield reliable, good
outcomes, but (as discussed above) there may still be opportunities
for further optimization in the various steps, should investigators
be interested to pursue those.
442
Victoria Keros and Barry J. Fuller
the world, the debate continues about which (or, if either) technique is superior for oocyte cryopreservation [55–58]. Recent systematic reviews in human oocyte cryopreservation comparing
either slow cooling methods or VS techniques found some evidence
that oocyte recovery, fertilization, and embryo development were
higher in the VS groups [31, 51, 59–61]. Due to different requirements in operator skills, process times, equipment availability, and
species-specific factors in oocyte biology, no single cryopreservation method is likely to be suitable in all situations, for all species or
for all developmental stages of oocytes. Many ancillary factors such
as oocyte quality and selection, hormonal stimulation regime, and
in vitro manipulation conditions can impact on cryopreservation
outcomes [6, 50, 62]. Even if VS is superior for oocyte cryopreservation, further studies on the fundamental biophysics of cryogenic
exposure could optimize both CRSC and VS protocols. As far as
can be assessed from current information, oocyte cryopreservation
does not impact in a negative way on birth abnormalities
[48, 50]. Oocyte cryopreservation has moved away from assignment as an experimental procedure, towards recognition of the true
value of this powerful technique with far-reaching potential in
reproductive technologies. As we approach the 2020’s, there is a
highly significant switch to VS for those centres performing oocyte
cryopreservation, such that, for example, in the UK and Scandinavia, none are now using CRSC (Fuller, Keros personal communication 2019). Therefore in this chapter, we shall concentrate on
providing details of the VS method. However still some scientists
are interested in details and principles of slow cooling, especially for
animal oocyte cryobanking. Thus we also present a robust method
and protocol details for murine oocyte CRSC [2]. Detailed explanation of the Cryotop
®
—Open System method (Kitazato Biopharma, Shizuoka, Japan)—successfully applied worldwide for
human oocyte VS can be found on the Kitazato company’s homepage (https://www.kitazato-dibimed.com/wp-content/uploads/
CRYOTOP_SAFETYKIT_A5_2019_LOW.pdf).
Two methods of oocyte cryopreservation are described below,
with the necessary technical details to introduce these into a standard laboratory setting and which have been developed over several
years for murine oocytes. One method is for slow controlled rate
cooling, and the other is a VS method. They can yield reliable, good
outcomes, but (as discussed above) there may still be opportunities
for further optimization in the various steps, should investigators
be interested to pursue those.
442
Victoria Keros and Barry J. Fuller