From the Guidelines
Transferring a 1-week embryo with 50% mosaicism, specifically 50% XY and 22 chromosome abnormalities, is not a recommended course of action due to the potential risks and uncertainties associated with mosaicism. The decision to transfer such an embryo should be made with caution and after thorough consultation with a reproductive endocrinologist and a genetic counselor, as the success rates with mosaic embryos vary widely depending on which chromosome is affected and the percentage of abnormal cells 1.
Key Considerations
- Mosaicism indicates that some cells have normal chromosomes while others have abnormalities, which may affect development potential.
- The incidence of mosaic RATs identified at the time of CVS is 0.6%, and only 2.53% of these cases were confirmed through amniocentesis 1.
- The rare cases of mosaicism confirmed by amniocentesis are associated with a wide range of phenotypic consequences.
- Pretest counseling is critical in allowing individuals to make well-informed decisions about pursuing preimplantation genetic testing (PGT) or other reproductive options 2, 3.
Recommendations
- Couples should be fully informed of all risks during PGT-M, including possible gamete and embryo damage, and the uncertainty of potentially developing mosaic embryos 3.
- A thorough risk assessment and informed choice should be made before implementing assisted reproductive technology (ART) 3.
- Consultation with a genetics health care professional is prudent in any case when PGT is being considered as an alternative to diagnostic testing 1.
Next Steps
- Consult with a reproductive endocrinologist and a genetic counselor to discuss the specific risks of transferring this embryo and to determine the best course of action.
- Consider the advantages and disadvantages of genetic diagnosis methods, such as prenatal diagnosis and PGT-M, and make an informed decision based on individual circumstances 3.
From the Research
Embryo Viability with Mosaicism
- A 1-week embryo with mosaicism, specifically 50% XY and 22 chromosome abnormalities, may be considered for transfer, but thorough genetic counseling is recommended 4, 5.
- Studies have shown that mosaic results obtained through preimplantation genetic testing for aneuploidy do not necessarily pose an increased risk to ongoing pregnancies or newborns 4.
- However, chromosomal anomalies can compromise the viability of embryos and are responsible for a large proportion of miscarriages and congenital disorders 6.
Preimplantation Genetic Testing
- Preimplantation genetic testing (PGT) is used to identify genetic abnormalities in embryos prior to their implantation, including chromosomal abnormalities, monogenic disorders, and structural rearrangements 7.
- PGT can detect chromosomal mosaicism, which is the presence of a mix of normal and abnormal cells in an embryo 6, 7.
- The detection of mosaicism can present challenges for clinicians in developing policies regarding transfer and storage of such embryos, as well as in providing genetic counseling for patients 5.
Clinical Considerations
- Thorough genetic counseling is essential for patients considering mosaic embryo transfer to assess and explain potential prenatal, neonatal, and long-term risks 4, 5.
- Clinicians must weigh the potential benefits and risks of transferring a mosaic embryo, taking into account the specific characteristics of the embryo and the patient's individual circumstances 4, 6, 5.