Mice oocyte vitrification does not influence fertilization by DNA fragmented sperms but reduces blastocyst formation

Introduction and Objectives: Nowadays, the vitrification of oocytes widely used in assisted reproductive technology. Some studies show that vitrification can reduce the quality of embryo or blastocysts rate but in general does not have any effect on implantation and live birth rate. We tried to answer this question, is it the same embryo development potential if the oocyte was fertilized with DNA fragmented sperm (DFS).Material and Methods: This ongoing project was conducted on DBA/2 mouse model of sperm DNA damage by intraperitoneal injection of tert-Butyl hydroperoxide (TBHP) at a dose of 203μmol per 100gr weight for 14 days, then the epidydimal sperm were used for in vitro fertilization (IVF). For control, no treatment was done. Cumulus-Oocyte-Complex (COC) was derived from oviducts of female DBA/2 mouse and superovulated with pregnant mare’s serum gonadotropin (PMSG) and continue with human chronic gonadotropin (HCG) after 48h. The COCs were randomly divided for verification and using fresh and conjugated with DFS and intact untreated sperms. For vitrification, COCs were washed and put in 7.5% Ethylene glycol (EG) +7.5% Dimethyl sulfoxide (DMSO) for 5 minutes, then exposed to 15% EG +15% DMSO + 0.5mol/L sucrose for 1 minute and saved in LN2 on Cryotop. For warming, vitrified oocytes were washed with 3 different concentrations of sucrose contain 1mol/L, 0.5mol/L and 0.25mol/L for 1, 3 and 3 minutes, respectively.Results: There was no significant difference in fertilization rate between non-vitrified and vitrified with untreated and DNA fragmented sperms, but blastocyst formation rate decreased in the vitrified COCs compared to the non-vitrified group when fertilized with both untreated and treated sperms.Conclusion: It seems regardless of sperm DNA fragmentation, which may be repaired in the first steps of fertilization, the reduction of blastocyst rate is due to oocyte damage in the process of vitrification per se.