In vitro development of vitrified bovine oocytes is correlated with mathematical predictions of cooling and warming rates during cryopreservation, storage and sample removal

MARINA SANSINENA ; MARIA VICTORIA SANTOS; JORGE CHIRIFE ; NOEMI ZARITZKY

REPRODUCTIVE BIOMEDICINE ONLINE

REPRODUCTIVE HEALTHCARE LTD

Lugar: Amsterdam; Año: 2018 vol. 36 p. 500 - 507

1472-6483

Heat transfer during cooling and warming is difficult to measure in cryo-devices; mathematical modelling is an alternative method that can describethese processes. In this study, we tested the validity of one such model by assessing in-vitro development of vitrified and warmed bovine oocytes afterparthenogenetic activation and culture. The viability of oocytes vitrified in four different cryo-devices was assessed. Consistent with modelling predictions,oocytes vitrified using cryo-devices with the highest modelled cooling rates had significantly (P < 0.05) better cleavage and blastocyst formationrates. We then evaluated a two-step sample removal process, in which oocytes were held in nitrogen vapour for 15 s to simulate sample identificationduring clinical application, before being removed completely and warmed. Oocytes exposed to this procedure showed reduced developmental potential,according to the model, owing to thermodynamic instability and devitrification at relatively low temperatures. These findings suggest that cryodeviceselection and handling, including method of removal from nitrogen storage, are critical to survival of vitrified oocytes. Limitations of the study include use of parthenogenetically activated rather than fertilized ova and lack of physical measurement of recrystallization. We suggest mathematical modelling could be used to predict the effect of critical steps in cryopreservation