What is the implication of a Preimplantation Genetic Testing for Aneuploidy (PGT-A) result showing Mosaicism (MOSAICO) with XY -22 chromosome abnormality, with 50% viable cells?

From the Guidelines

PGT-A results showing MOSAICO XY -22(M:50%) indicate a male embryo with mosaic monosomy of chromosome 22 affecting approximately 50% of the cells tested, and this embryo may be considered viable for transfer, but with caution. I recommend discussing this embryo with your reproductive endocrinologist before making a decision about transfer. Mosaic embryos contain a mixture of normal and abnormal cells, and in this case, half the cells are missing one copy of chromosome 22. While historically such embryos might have been discarded, current evidence suggests that mosaic embryos can sometimes result in healthy pregnancies, as the abnormal cells may be confined to the placenta or may be eliminated during development 1. If you choose to transfer this embryo, genetic counseling is advisable to understand potential risks, and enhanced prenatal testing such as NIPT (non-invasive prenatal testing) and detailed ultrasounds would be recommended during pregnancy. The decision to transfer should consider factors like your age, fertility history, and whether other euploid (chromosomally normal) embryos are available. The 50% mosaicism level is considered moderate, and some clinics use a threshold of 20-80% mosaicism when considering embryos for transfer. It is essential to weigh the potential risks and benefits of transferring this embryo, considering the possibility of a healthy pregnancy, against the potential risks of miscarriage, failed pregnancy, or birth defects 1. Ultimately, the decision to transfer this embryo should be made after careful consideration and consultation with a reproductive endocrinologist and genetic counselor.

Some key points to consider:

• Mosaic embryos can result in healthy pregnancies, but there is also a risk of miscarriage, failed pregnancy, or birth defects
• Genetic counseling is essential to understand the potential risks and benefits of transferring this embryo
• Enhanced prenatal testing, such as NIPT and detailed ultrasounds, would be recommended during pregnancy
• The decision to transfer should consider factors like age, fertility history, and the availability of other euploid embryos
• The 50% mosaicism level is considered moderate, and some clinics use a threshold of 20-80% mosaicism when considering embryos for transfer.

From the Research

Implication of PGT-A Result Showing Mosaicism with XY -22 Chromosome Abnormality

• A PGT-A result showing mosaicism (MOSAICO) with XY -22 chromosome abnormality and 50% viable cells indicates the presence of both euploid and aneuploid cells in the embryo 2, 3.
• The clinical significance of mosaicism in human blastocysts is still a topic of debate, with some studies suggesting that mosaic embryos can lead to healthy live births, while others report reduced ongoing pregnancy rates compared to euploid embryos 3, 4.
• The transfer of mosaic embryos with less than 50% aneuploidy has been shown to yield a live birth rate similar to euploid embryos, which has led to a shift in current PGT-A practice 4.
• However, there is still a lack of long-term outcome data following mosaic aneuploid embryo transfer, and the risk of miscarriage, fetal mosaic aneuploidy, and uniparental disomy cannot be ruled out 5, 6.

Considerations for Embryo Transfer

• The decision to transfer a mosaic embryo should be made on a case-by-case basis, taking into account the specific chromosomal abnormality, the percentage of mosaicism, and the patient's individual circumstances 2, 6.
• Proper genetic counseling is essential to inform patients of the potential risks and benefits associated with mosaic embryo transfer 6.
• The development of risk scores for each chromosome may help prioritize which mosaic embryos should be considered for transfer, but further research is needed to establish clear guidelines for selecting mosaic embryos suitable for transfer 5, 4.