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 are increasingly transferred when no euploid embryos are available, but success rates can vary depending on the type and extent of mosaicism.
A new study by Jin et al. (2026) compared pregnancy outcomes across different mosaic types, including low vs high level, segmental vs whole chromosome, and monosomy vs trisomy. They also looked at maternal complications and birth defects to assess safety after transfer.
Check my complete guide to mosaic embryos to learn more about mosaics, or my complete guide to PGT-A to get more background on PGT-A.
🔗 Original studies are referenced in this post or within the linked Remembryo posts.
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Study details
- Study type: Retrospective cohort study conducted at a single academic fertility center in China between 2018 and 2023.
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Participants: 434 single transfers using mosaic embryos and 868 euploid transfers (propensity score matching was used to match maternal age, BMI, AMH, etc. at a 1:2 ratio). Average age was about 34.
- Mosaic level: 375 low level (≤50%) and 59 high level (>50%). Mosaics were defined as having 30-70% abnormal cells.
- Type of abnormality: 204 segmental mosaics (91 duplications and 113 deletions), 139 whole chromosome mosaics (74 trisomy and 65 monosomy), and 91 complex mosaics (2 or more abnormalities)
- Embryos: All embryos underwent PGT-A using next-generation sequencing. Only day 4, 5 or 6 blastocysts graded 4BC or higher were biopsied (most were day 4 or 5, expansion 4 and BB quality).
All mosaics compared to euploids
All mosaics vs euploids: Lower success rates. This group compared all mosaics in the study.
- Lower live birth rate (44.70% vs 51.73%, odds ratio [95% CI]: 0.76 [0.60-0.96])
- Higher miscarriage rate (18.11% vs 11.65%, odds ratio [95% CI]: 1.65 [1.08-2.52])
Low or high level mosaics compared to euploids
Low level mosaics vs euploids: Higher miscarriage rate. This group compared mosaics with ≤50% abnormal cells.
- Higher miscarriage rate (17.43% vs 11.70%, odds ratio [95% CI]: 1.59 [1.01-2.50])
- No other statistically significant differences were reported.
High level mosaics vs euploids: Lower success rates. This group compared mosaics with >50% abnormal cells.
- Lower clinical pregnancy rate (42.37% vs 74.58%, odds ratio [95% CI]: 0.25 [0.13-0.48])
- Lower live birth rate (30.51% vs 61.86%, odds ratio [95% CI]: 0.27 [0.14-0.53])
Segmental mosaics compared to euploids
Segmental mosaics (all) vs euploids: No significant differences. This group compared all segmental mosaics, which involved either a duplication or deletion of a small segment of a chromosome.
- No difference in clinical pregnancy rate (62.25% vs 60.78%, p= 0.558)
- No difference in live birth rate (49.02% vs 49.26%, p= 0.954)
- No difference in miscarriage rate (18.90% vs 12.90%, p= 0.155)
Segmental mosaics (duplication) vs euploids: No significant differences. This group compared only segmental mosaics with a duplication of a chromosomal segment.
- No difference in clinical pregnancy rate (69.23% vs 61.54%, p= 0.204)
- No difference in live birth rate (54.95% vs 49.45%, p= 0.353)
- No difference in miscarriage rate (17.46% vs 13.39%, p= 0.623)
Segmental mosaics (deletion) vs euploids: No significant differences. This group compared only segmental mosaics with a deletion of a chromosomal segment.
- No difference in clinical pregnancy rate (56.64% vs 60.18%, p= 0.599)
- No difference in live birth rate (44.25% vs 49.12%, p= 0.400)
- No difference in miscarriage rate (20.31% vs 12.50%, p= 0.148)
Whole chromosome mosaics compared to euploids
Whole chromosome mosaics (all) vs euploids: Lower success rates. This group compared all whole chromosome mosaics, which involve either a missing (monosomy) or extra (trisomy) whole chromosome.
- Lower clinical pregnancy rate (50.36% vs 61.87%, p = 0.039)
- Lower live birth rate (41.01% vs 53.24%, p = 0.019)
- No difference in miscarriage rate (17.14% vs 8.72%, p = 0.064)
Whole chromosome mosaics (trisomy) vs euploids: Lower success rates. This group compared whole chromosome mosaics with an extra whole chromosome (trisomy).
- Lower clinical pregnancy rate (47.30% vs 64.86%, p= 0.011)
- Lower live birth rate (32.43% vs 57.43%, p< 0.001)
- Higher miscarriage rate (28.57% vs 6.25%, p= 0.001)
Whole chromosome mosaics (monosomy) vs euploids: No significant differences. This group compared whole chromosome mosaics with a missing whole chromosome (monosomy).
- No difference in clinical pregnancy rate (53.85% vs 58.46%, p= 0.625)
- No difference in live birth rate (50.77% vs 48.46%, p= 0.765)
- No difference in miscarriage rate (5.71% vs 11.84%, p= 0.326)
Complex mosaics compared to euploids
Complex chromosome mosaics vs euploids: Lower success rates. This group compared complex mosaics with 2 or more mosaic chromosomal abnormalities.
- Lower clinical pregnancy rate (50.55% vs 66.48%, p= 0.013)
- Lower live birth rate (40.66% vs 54.95%, p= 0.029)
- No difference in miscarriage rate (17.39% vs 13.22%, p= 0.494)
No increased risk of pregnancy complications or birth defects with mosaic embryos
Across all mosaic subgroups, there were no significant differences in pregnancy complications (gestational diabetes, gestational hypertension, or preeclampsia) or congenital anomalies compared with euploid embryos.
Conclusion
Overall, mosaic embryo transfers had lower live birth rates and higher miscarriage rates compared with euploid embryos. But the results depended on the type and level of mosaicism:
- Low-level mosaics had a slightly higher miscarriage rate.
- High-level mosaics had much lower pregnancy and live birth rates.
- Segmental mosaics, including both duplications and deletions, were similar to euploid embryos.
- Whole chromosome mosaics had lower success rates, mostly driven by trisomy mosaics. Monosomy mosaics didn’t show differences compared to euploids.
- Complex mosaics had lower live birth and clinical pregnancy rates.
Importantly, across all mosaic groups, there was no increase in pregnancy complications or birth defects.
The results showed that monosomy is better tolerated compared to trisomy. This may be because cells missing a chromosome are more likely to be removed early in development, leaving mostly normal cells, while cells with an extra chromosome may be more likely to persist past implantation and increase the risk of miscarriage.
Overall, these results are similar to other mosaic embryo studies. In many studies, overall differences between euploid and mosaic embryos were mainly driven by high-level mosaics, while low-level mosaics often had live birth rates similar to euploid embryos and no significant difference in miscarriage rates. Segmental mosaics also tend to have outcomes comparable to euploids.
Together, these results suggest that not all mosaic embryos carry the same risk, and outcomes depend on the level and type of mosaicism.
Limitations include the retrospective single-center design, no genetic testing of newborns, small sample sizes in some subgroups, and possible remaining bias since mosaic embryos were only transferred in patients without available euploid embryos.
Want to read more about mosaic embryo success rates?
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. Read more.
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. Read 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. Read more.
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. Read more.
Reference
About Embryoman
Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.