A 2026 study found that mosaic embryo outcomes vary by type and level, with high-level and trisomy mosaics showing lower success rates, while segmental mosaics had outcomes similar to euploids.
Mosaic embryos
In a 2025 study, researchers masked mosaic PGT-A results and found that mosaic reporting did not meaningfully improve embryo selection or live birth prediction beyond standard criteria, suggesting that PGT-A’s main clinical value lies in identifying clearly aneuploid embryos.
Using a new non-toxic imaging method, researchers watched living human embryos divide in real time and discovered that chromosome separation errors linked to mosaicism can arise even at the blastocyst stage, showing that mosaicism is a dynamic process rather than one confined to early development.
This post traces the evolution of PGT-A testing in IVF, from early FISH and microarray methods to modern NGS and emerging technologies like nanopore sequencing, highlighting how each advancement improved accuracy, speed, and embryo assessment.
A 2025 study shows that segmental abnormalities detected by PGT-A in the trophectoderm don’t always match the ICM, suggesting that these embryos may still be viable for transfer.
Researchers in a 2025 study performed PGT-A on whole embryos, including arrested embryos and different developmental stages, finding high rates of euploidy.
A 2025 study re-analyzed embryos that tested as mosaic by NGS-based PGT-A using SNP karyotyping and found that one-third of those “mosaics” were actually uniformly aneuploid.
A 2025 opinion article highlights some of the issues with PGT-A, mainly its uncertain benefit, technical flaws, high costs, and the risk of discarding potentially viable embryos.
Researchers in 2024 report on live births after segmental aneuploid transfers, finding that they have similar rates as high level mosaic segmental aneuploids.
A 2024 study performed a more sensitive type of PGT-A by analyzing single cells, finding that nearly all blastocysts and fetal tissue contain some level of mosaicism.
The ASRM has released their 2024 committee opinion on the use of PGT-A, covering the use of PGT-A for patients with a good prognosis, advanced age, donor eggs, recurrent pregnancy loss and more.
Researchers in a 2024 study found no health problems in children born from mosaic embryo transfers, with an average age of 3 years. They also found no differences in obstetric outcomes between mosaic and euploid transfers.
Researchers in a 2023 study found increased miscarriage rates with mosaic embryo transfers compared to euploids, with no differences in neonatal outcomes.
Mosaic embryos are able to self-correct and result in a normal baby the majority of the time, without evidence of any chromosomal abnormalities, however there are seven cases (as of 2023, to my knowledge) of a mosaic embryo leading to a birth with the same affected chromosome.
Evidence up to 2022 shows that a single PGT-A biopsy is highly concordant (similar) with the rest of the embryo when the embryo is aneuploid or euploid, but not when it’s mosaic or segmental.
Researchers in a 2021 study performed a clinical trial and found that low and moderate level mosaic embryos have comparable pregnancy outcomes to euploid embryo transfers.
Researchers in a 2021 study investigated “self-correction” in a stem cell-based model for mosaic embryos and found that aneuploid cells in a mosaic are more likely to change into trophectoderm cells or die, while euploid cells accumulate in the ICM.
Researchers in a 2021 study compared outcomes from 1,000 mosaic embryo transfers, consisting of high and low level, as well as whole chromosome or segmental mosaics.
This post covers mosaic embryos, including their definition, frequency after PGT-A, mosaic embryo levels (low level, high level), mosaic embryo types (whole chromosome, segmental), current guidelines for transfer, potential for self-correction, and success rates.
This post covers PGT-A, including how it works, how accurate it is, whether it can damage embryos, how to read PGT-A reports, success rates, mosaic embryos, and why even euploid embryos sometimes fail.