Introduction
Preimplantation genetic testing for aneuploidy (PGT-A) is widely used to detect chromosomal abnormalities in embryos prior to implantation to improve the chances of a successful pregnancy. However, detecting mosaic embryos—those containing a mixture of normal and abnormal cells—presents considerable challenges. Reported mosaicism rates vary widely between 2% and 35.6%, impacted by biological complexity and technical limitations. Distinguishing true mosaicism from false positives caused by artifacts during testing remains difficult, complicating clinical decisions about whether to transfer these embryos. Additionally, understanding the origin of the chromosomal aberrations—whether from meiotic (germline) or mitotic (post-fertilization cell division) errors—and their implications for clinical outcomes is limited. This study aimed to reduce false-positive diagnoses of mosaic embryos by analyzing parental and cell-division origins of chromosomal abnormalities, thereby enhancing embryo selection and transfer strategies.
Study Design and Methods
This retrospective study analyzed a large dataset comprising 9,062 PGT-A results alongside 8,645 amniocentesis prenatal samples collected between 2021 and 2024 to examine differences in mosaicism prevalence between preimplantation and prenatal diagnoses. Furthermore, in 2024, an innovative parental haplotype trace (PH-trace) algorithm was applied to 1,221 consecutive PGT-A and PGT for monogenic disorders (PGT-M) results from 259 patients over 304 treatment cycles. The PH-trace approach identifies the parental origin of chromosomal aberrations by assessing biallelic homozygous SNPs that normally show equal allele frequency in euploid embryos but demonstrate bias toward maternal or paternal alleles in affected embryos. Using this bias, an “uneven score” quantifies whether the aberration likely arose from one parent or is an artifact. Receiver operating characteristic (ROC) curve analysis was conducted to define thresholds distinguishing true mosaicism from false positives. Heterozygous parental SNPs were similarly used to determine whether chromosomal errors originated during mitosis (post-fertilization cell divisions) or meiosis (gamete formation). The methodology was validated through multi-site re-biopsies of 36 donated embryos and evaluation of clinical outcomes from 19 mosaic embryo transfers.
Key Findings
The analysis revealed a significantly higher mosaicism rate detected by PGT-A compared to prenatal testing (12.2% vs 0.9%, respectively; P < 0.001). Importantly, parental origin analysis reclassified over half (52.6%) of embryos initially diagnosed as mosaic back to euploid status, improving embryo utilization rates by 8.6%. Most genuine mosaic cases were attributable to mitotic errors, which tend to have different clinical implications than meiotic errors. Multi-site re-biopsy validation showed that 94.1% of predicted false-positive copy-number variations (CNVs) were not present upon subsequent testing, supporting the robustness of the PH-trace method. Conversely, 71.4% of CNVs identified with parental bias were repeatedly detected, confirming their true biological origin. Among mosaic embryos that successfully resulted in live births, two-thirds were false positives and approximately one-fifth arose from mitotic errors, highlighting important considerations for embryo transfer prioritization.
Implications for Clinical Practice
This two-tiered analytical approach using PH-trace and cell-division analysis offers clinicians a powerful tool to reduce diagnostic uncertainty related to mosaicism in embryos. By accurately excluding false-positive mosaic embryos, more viable euploid embryos can be confidently transferred, potentially increasing successful pregnancy rates. Additionally, differentiating whether mosaicism stems from mitotic or meiotic errors can inform risk assessments and counseling for patients considering mosaic embryo transfer. This evidence-based framework helps embryologists prioritize embryo transfer decisions more effectively and may lead to fewer in vitro fertilization (IVF) cycles and reduced costs for patients, particularly those with limited euploid embryo availability.
Limitations and Future Directions
The detection method depends on the availability of sufficient informative parental SNPs—generally more than 30 per chromosomal aberration—limiting its application in cases with limited genetic markers. Moreover, long-term clinical outcomes related to mosaic embryos reclassified using this technique require continued follow-up to fully understand neonatal and developmental impacts. Future research should aim to validate these findings in larger, prospective cohorts and explore integration with other genomic technologies to enhance sensitivity and specificity further.
Conclusion
This study demonstrates that application of parental haplotype tracing combined with cell-division origin analysis substantially improves the accuracy of mosaic embryo diagnoses in PGT-A. Reducing false-positive identification of mosaicism expands usable embryo pools and facilitates more informed embryo transfer decisions. Ultimately, such advanced genetic analytical strategies hold promise to optimize IVF outcomes, reduce patient burden, and contribute to personalized reproductive medicine.
Funding and Disclosures
This research was supported by national and municipal scientific foundations and medical talent projects in China, including the National Natural Science Foundation of China and Chongqing municipal funds. The authors declare no competing interests.
Reference
Zhang Q, Liu G, Xiang Y, Zou Y, Chen Y, Xia Y, Xiong S, Fu T, Wang J, Jiang Y, Xiong J, Zhang X, Lu S, Liu D, Huang G, Lin T. Parental and cell-division origin analysis to reduce false-positives in mosaic embryos for preimplantation genetic testing. Hum Reprod Open. 2025 Dec 1;2025(4):hoaf075. doi:10.1093/hropen/hoaf075. PMID:41426978; PMCID:PMC12714397.