ABSTRACT
OBJECTIVE: To determine whether euploidy rates and blastocyst development differ in a continuous culture medium under different CO2 concentrations. DESIGN AND METHOD: A single-center retrospective study was performed from July 2018 to October 2019 including 44 fresh cycles with at least four fresh mature oocytes (MII) without severe male factor infertility. Sibling MII were injected and cultured in Global®Total®LP under 6.0% (pHe = 7.374 ± 0.014) or 7.0% (pHe = 7.300 ± 0.013) CO2, 5.0% O2, and 89.0% or 88.0% N2. Analyzed variables were normally fertilized oocytes (2PN), cleavage rate, blastulation rate on day 5/2PN, usable blastocyst (blastocysts biopsied/2PN), and euploidy rates. Blastocyst's trophectoderm biopsy was performed on day 5, 6, or 7 for genetic testing and mitochondrial DNA (mtDNA) quantification by next-generation sequencing. RESULTS: Women's mean age was 33.0 ± 6.6 years old. From a total of 604 MII, no differences were found in normal fertilization and cleavage rates on day 3 between 6.0 and 7.0% CO2 (72.3% vs 67.1%, p = 0.169 and 96.6% vs 96.3%, p = 0.897, respectively). Blastulation rate on day 5/2PN was comparable between 6.0 and 7.0% CO2 (68.1% vs 64.2%, p = 0.409). Although usable blastocyst rate was not different (54.3% vs 55.3%, p = 0.922), total euploidy rates differed significantly (58.7% vs 42.8%, p = 0.016) between 6.0% and 7.0% CO2, respectively. The mean blastocyst mtDNA content was significantly lower in 6.0% CO2 (30.4 ± 9.1 vs 32.9 ± 10.3, p = 0.037). CONCLUSION: Blastocyst development is not affected when embryos are cultured in vitro at 6.0% or 7.0% CO2, while euploidy rates are significantly decreased at a higher CO2 concentration, therefore at a lower pHe.
Subject(s)
Blastocyst/cytology , Carbon Dioxide/pharmacology , Chromosome Aberrations/drug effects , Embryo Culture Techniques/methods , Fertilization in Vitro/methods , Oocytes/cytology , Adult , Blastocyst/drug effects , Embryo Implantation , Embryo Transfer , Female , Genetic Testing , Humans , Hydrogen-Ion Concentration , Male , Oocytes/drug effects , Pregnancy , Preimplantation Diagnosis/methods , Retrospective Studies , SiblingsABSTRACT
The open carrier system (OC) is used for vitrification due to its high efficiency in preserving female fertility, but concerns remain that it bears possible risks of cross-contamination. Closed carrier systems (CC) could be an alternative to the OC to increase safety. However, the viability and developmental competence of vitrified/warmed (VW) oocytes using the CC were significantly lower than with OC. We aimed to improve the efficiency of the CC. Metaphase II oocytes were collected from mice after superovulation and subjected to in vitro fertilization after vitrification/warming. Increasing the cooling/warming rate and exposure time to cryoprotectants as key parameters for the CC effectively improved the survival rate and developmental competence of VW oocytes. When all the conditions that improved the outcomes were applied to the conventional CC, hereafter named the modified vitrification/warming procedure using CC (mVW-CC), the viability and developmental competence of VW oocytes were significantly improved as compared to those of VW oocytes in the CC. Furthermore, mVW-CC increased the spindle normality of VW oocytes, as well as the cell number of blastocysts developed from VW oocytes. Collectively, our mVW-CC optimized for mouse oocytes can be utilized for humans without concerns regarding possible cross-contamination during vitrification in the future.