JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):174
Poster Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263914

P-162. Morphological aspects and development of embryos used in the Mouse Embryo Assay (MEA)

Vera Lucia Langaro Amaral¹, Leticia Fronza Dias¹, Rafael Alonso Salvador¹, Alfred Paul Senn²

¹ Universidade do Vale do Itajai-UNIVALI - Itajai - SC – Brasil
² University of Geneva, Switzerland

Objective: This study aimed to evaluate the morphological aspects of mouse embryos and the criteria used for their selection and application in the Mouse Embryo Assay (MEA). The study was carried out by following the implementation of the MEA test by a trained technician responsible for approving batches of culture media and materials used in assisted human reproduction
Methods: A total of 61 B6D2F1 female mice (hybrids of C57BL/6J and DBA/2J) were used. Superovulation was induced with 10 IU of eCG (Equine Chorionic Gonadotropin – Novormon^®, Syntex), followed 48 hours later by 10 IU of hCG (Human Chorionic Gonadotropin – Vetecor^®, HertapeCalier). The females were then mated with males of the same strain. Embryos were collected 45 hours after mating, targeting the 2-cell stage. Fourteen embryo collections were performed, yielding a total of 998 embryos and structures, which were distributed into four groups: MEA (n=184), Control (n=257), Altered Morphology (n=106), and Discarded (n=451). The structures in the Discarded group showed no capacity for culture or embryonic development. Embryos from the Control and Altered Morphology groups were cultured in Continuous Single Culture Complete medium (CSCM-C, Irvine Scientific, Santa Ana, CA, USA) in an incubator at 37.2ºC with 6.6% CO₂ for five days.
Results: The results were expressed as the average number of embryos per female and the rate of expanded blastocyst formation per group. Among the 998 items analyzed, the average per female was 7.22 morphologically normal embryos, 1.73 morphologically altered embryos, and 7.4 non-viable structures. The expanded blastocyst formation rates were 96.5% in the Control group, 96.4% in the MEA group, and 93.4% in the Altered Morphology group. The most frequent morphological alterations observed were blastomere asymmetry (n=49; 46.2%), rounded blastomeres (n=40; 37.7%), rounded blastomeres with asymmetry (n=8; 7.5%), and zona pellucida defects (n=9; 8.5%). Regarding the discarded structures, the most common findings were loose zona pellucida (n=117; 27.9%), free blastomeres (n=95; 21.1%), unfertilized oocytes (n=92; 20.4%), degenerated oocytes (n=82; 18.1%), fragmented oocytes (n=57; 12.6%), and 4-cell embryos (n=8; 1.8%). No statistically significant differences were found between the Control, MEA, and Altered Morphology groups (p=0.19), indicating that embryos with morphological alterations still have developmental potential to reach the expanded blastocyst stage.
Conclusion: Thus, visual screening alone should not be considered an absolute criterion for approving or discarding embryos for the MEA test. The findings support the need for more robust embryo selection techniques in MEA, including additional blastocyst evaluation parameters such as cell number, hatching, and implantation. The effectiveness of the MEA model in ensuring the absence of toxicity and long-term safety for embryos and offspring remains a topic for further investigation.