JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):176
Poster Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263912

P-164. Mosaic Embryos: Potential Implications in Reproductive Medicine

Isabela Ferreira Torres¹, Gabriela Neves Cunha¹, Paula Paiva Canabrava¹, Ana Márcia de Miranda Cota²

¹ Faculdade Ciências Médicas de Minas Gerais - Belo Horizonte - Minas Gerais – Brasil
² Departamento de Reproducao da Rede Mater Dei de Saude - Belo Horizonte – MG - Brasil

Objective: To conduct an updated literature review to assess the implantation rates and reproductive outcomes following the transfer of mosaic embryos in assisted reproductive technologies.
Methods: This integrative literature review performed a search using PubMed and Cochrane databases. The keywords used were "Embryonic Mosaicism", "Assisted Reproductive Technology" and "Embryo Implantation". The research criteria included articles in English, published between 2020 and 2025. The exclusion criteria were articles that required payment and case reports. Nineteen articles were included in this review.
Results: Contemporary reproductive medicine seeks to select embryos with higher potential for implantation and healthy development through technologies such as morphological embryo assessment and preimplantation genetic testing for aneuploidy (PGT-A). With advances in biopsy techniques and sensitivity of genomic analysis methods, it has become possible to identify a category distinct from euploid embryos: mosaic embryos. Embryonic mosaicism is the presence of two or more cell lines with different chromosomal complements within the same embryo. The American Society for Reproductive Medicine (ASRM) estimates that 2% to 20% of embryos analyzed through PGT-A present some degree of mosaicism. Currently, guidelines from ASRM (2023) and the European Society of Human Reproduction and Embryology (ESHRE; 2022) acknowledge the possibility of transferring mosaic embryos in cases where no euploid embryos are available. These guidelines recommend a thorough evaluation of the mosaicism's type and extension (low or high percentage of aneuploid cells), as well as the exclusion of mosaics involving chromosomal abnormalities of severe syndromes. The decision should include the patient and must be supported by appropriate genetic counseling. In the analyzed studies, mosaic embryos exhibited lower implantation rates and poorer reproductive outcomes, including ongoing pregnancy and live birth rates, compared with euploid embryos. However, the transfer of mosaic embryos, especially those with low-level mosaicism, can lead to healthy euploid live births. These findings represent validated clinical outcomes for women who do not have fully euploid embryos available and for patients with poor ovarian response. A study published in 2020 revealed an inferior implantation rate in mosaic embryos (51.8%) compared to euploid embryos (65.7%). Additionally, a reduced ongoing pregnancy rate was observed (47.0% vs. 64.8%). In this research, all newborns resulting from mosaic embryos presented normal karyotypes and no detectable congenital anomalies, suggesting the possibility of self-correction during embryonic development. The type of chromosomal abnormality (whole, segmental, or complex) and the level of the embryo's mosaicism didn't have a significant impact on clinical outcomes. Another study reported similar findings: the group of patients who underwent mosaic embryo transfer showed lower implantation and ongoing pregnancy rates compared to the control group, who received euploid embryos. Mosaic embryos were also associated with higher spontaneous miscarriage rates, especially in cases involving numerical chromosomal abnormalities. The same study concluded that embryos with single segmental mosaicism exhibited lower miscarriage rates and better reproductive outcomes than those with numerical abnormalities. It also compared the mosaic embryo group to another group of patients who underwent embryo transfer without PGT-A, and found no statistically significant differences in the outcomes. This highlighted the potential for false-positive mosaicism diagnoses through PGT-A, as well as the evidence of discrepancies between the trophectoderm and the inner cell mass. These findings suggest that such tests may not accurately represent the embryo as a whole.
Conclusion: Although mosaic embryos show lower implantation, ongoing pregnancy, and live birth rates compared to euploid embryos, their transfer can result in healthy live births. This represents a possibility for patients with poor ovarian response or low euploid embryos, as ASRM and ESHRE guidelines affirm. Careful analyses of the type and extent of mosaicism, along with appropriate genetic counseling, is essential.