A mosaic embryo contains both chromosomally normal (euploid) and abnormal (aneuploid) cells in the same embryo. This is identified through PGT-A (Preimplantation Genetic Testing for Aneuploidy).

Levels of Mosaicism

Low-level mosaic — 20–40% abnormal cells
High-level mosaic — 40–80% abnormal cells
> 80% — considered aneuploid
< 20% — considered euploid

Should You Transfer a Mosaic Embryo?

Priority order: Transfer euploid embryos first. If none available, consider mosaic embryos — prefer low-level over high-level, and avoid chromosomes associated with viable trisomy (13, 18, 21) or monosomy X.

Evidence Summary (PGDIS 2019, ESHRE 2020)

Mosaic embryos have ~20% lower pregnancy rate vs euploid
Higher miscarriage rate
Most live births from mosaic transfers have normal chromosomes (self-correction in early embryo)
No increased congenital abnormality reported vs euploid transfer

Factors to Consider

Maternal age (older patients have fewer euploid options)
Number of remaining euploid embryos
Mosaicism level and specific chromosomes involved
Couple's readiness and understanding
Genetic counseling essential

Prenatal Confirmation

If transferring mosaic, recommend NIPT + amniocentesis during pregnancy to confirm fetal chromosomes.

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Mosaic Embryos: Transfer or Not?

Levels of Mosaicism

Should You Transfer a Mosaic Embryo?

Evidence Summary (PGDIS 2019, ESHRE 2020)

Factors to Consider

Prenatal Confirmation

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