MATERIALS AND METHODS: Six 5x5 mm ovarian cortical pieces were harvested from each organ donor cadaver (n¼18 pieces from 3 donors; mean age 31AE8 years) and assigned to either open vitrification (OV) or closed vitrification (CV) in a paired design. Cryopreserved tissues were thawed 8-10 weeks later and evaluated on thaw (0h) and after 24-96h culture. Formalin fixed, paraffinembedded blocks were serially sectioned and primordial (pdf) and primary (pyf) follicle densities, % of pdf and pyf with DNA double-strand breaks (by gH2AX) and apoptotic cell death pathway activation (AC3) were determined.RESULTS: The data are summarized in Table 1. Compared to OV, pdf and pyf densities were similar in the CV group after thawing. Likewise, the percentages of apoptotic and DNA-damaged pdf did not differ between the OVand CV groups on the thaw day. However, the percentage of apoptotic pdf was significantly reduced in the CV group compared to the OV after 96h in culture (p¼0.03).CONCLUSIONS: Our results show that the newly developed CV system provides similar or better efficacy compared to open vitrification with human ovarian tissue. The mechanism of higher primordial follicle survival rate with CVafter 96h culture needs to be further explored. Having showed that the OV has similar efficacy to slow freezing with ovarian tissues (see abstract 2017-A-2005-ASRM), we propose that the CV method should become the standard method of ovarian tissue cryopreservation.

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