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Different CO2 settings (6.0% vs 7.0%) do have an impact on extracellular pH of culture medium (pHe) and euploidy rates rather than on blastocyst development: a sibling oocyte study

  • Assisted Reproduction Technologies
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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.

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Acknowledgements

We would like to thank Victor Lozoya García for his help and support with statistical evaluation and interpretation.

Author information

Authors and Affiliations

  1. ART Fertility Clinics, Abu Dhabi, United Arab Emirates

    Andrea Abdala, Ibrahim Elkhatib, Aşina Bayram, Ana Arnanz, Ahmed El-Damen, Laura Melado, Barbara Lawrenz, Human M. Fatemi & Neelke De Munck

  2. Obstetrical Department, Women’s University Hospital Tübingen, Tübingen, Germany

    Barbara Lawrenz

  3. IVI Foundation, Instituto de Investigación Sanitaria La Fe (IIS La Fe), Valencia, Spain

    Nicolás Garrido

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  1. Andrea Abdala
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Contributions

AAb, ND, HF: conception and design of the study; AAb, ND, IE, AA, AD, AB, LM, BL, HF: oocyte retrieval; ND, IE, AA, AD, AB, AAb: IVF and ICSI procedure and embryo evaluations; ND, IE, AA, AD, AB, AAb: blastocyst biopsy, tubing and freezing; AAb, NG: construction of the database and data interpretation; AAb: drafting the manuscript; ND, IE, AA, AD, AB, LM, BL, HF: critical review and final approval of the manuscript.

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Correspondence to Andrea Abdala.

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Abdala, A., Elkhatib, I., Bayram, A. et al. Different CO2 settings (6.0% vs 7.0%) do have an impact on extracellular pH of culture medium (pHe) and euploidy rates rather than on blastocyst development: a sibling oocyte study. J Assist Reprod Genet 38, 2915–2923 (2021). https://doi.org/10.1007/s10815-021-02303-0

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