Study reveals implantation and live birth rates for segmental aneuploid embryos

Stephanie Willson, MD, of the IVI RMA Global Research Alliance and a 2025 graduate of the Jefferson-RMA Fellowship Program, discussed new data on the reproductive potential of non-mosaic segmental aneuploid embryos at ASRM 2025 Scientific Congress. Her team’s double-blinded, multicenter non-selection study evaluated 176 single frozen embryo transfers to clarify how segmental aneuploid findings on preimplantation genetic testing should be interpreted in clinical practice. The results provide long-awaited prospective evidence on implantation, live birth rates, and the role of segmental aneuploid embryo transfer when no euploid embryos are available.

Contemporary OB/GYN: What prompted your team to focus on the reproductive potential of non-mosaic segmental aneuploid embryos, and how does this research build on what we already know about mosaicism and embryo selection?

Stephanie Willson, MD:

The use of preimplantation genetic testing (PGT) as a tool for embryo deselection has dramatically increased over the past several years. Newer technologies allow PGT to detect more subtle abnormalities (segmental aneuploidy), however, the clinical significance of these findings remain unclear.

Our interest in studying the reproductive potential of non-mosaic segmental aneuploid embryos was prompted by the inconsistency observed in rebiopsy studies as well as the lack of prospective data surrounding their transfer. Several rebiopsy studies have shown poor concordance for segmental aneuploidy, ranging from approximately 32% to 45%, compared with over 95% for euploid and aneuploid embryos. This low concordance may reflect true segmental aneuploidy, but also technical artifact or biological mosaicism, challenging the interpretation of the results without the context of clinical outcomes.

Prior to our study, there has been a lack of data investigating transfer outcomes of segmental aneuploid embryos in a blinded nature. Building on prior non-selection studies of mosaicism, our research sought to investigate the reproductive potential of non-mosaic segmental aneuploid embryos, helping clarify how these results should be interpreted, as well as assisting in patient counseling and embryo disposition.

Contemporary OB/GYN: Can you summarize the key findings from your double-blinded, multicenter non-selection study and what they reveal about implantation and live birth outcomes for these embryos?

Willson:

In our multicenter, double-blinded, non-selection study, 176 transfers were positive for segmental aneuploidy among over 7,600 single frozen embryo transfers initially classified as whole-chromosome aneuploid–negative. The results revealed that segmental aneuploid embryos are capable of implantation and live birth, but with significantly reduced success rates compared with the segmental aneuploid negative group. The live birth rate in the segmental aneuploid positive group was 27.3% per embryo transfer, compared to 60.0% in the negative group. Implantation rates were also decreased at 58.0% versus 78.6%, respectively.

Contemporary OB/GYN: How should clinicians interpret segmental aneuploid results from preimplantation genetic testing, and are there cases where transferring such embryos could be considered?

Willson:

These findings indicate that non-mosaic segmental aneuploid embryos possess reproductive potential, though at reduced rates compared with negative controls. The results support a shift away from automatic discarding of these embryos and provide an evidence-based approach for developing clinic policies regarding their management. Transfer of these segmental aneuploids are generally considered when no euploid embryos are available and should occur in close collaboration with a genetic counselor to ensure comprehensive patient counseling and informed decision making.

Contemporary OB/GYN: What are the main takeaways for fertility specialists when counseling patients who have only segmental aneuploid embryos available for transfer?

Willson:

When faced with transferring a segmental aneuploid embryo, although these embryos can lead to successful pregnancies, it is not risk-free given increased rates of pregnancy loss compared to euploid embryos. In addition, some segmental aneuploidies can be true to the embryo and fetus, resulting in other adverse outcomes. Providers should emphasize the importance of follow-up prenatal testing and work closely with genetic counselors who can provide patients with tailored counseling surrounding these findings.

Reference:

Willson S, Kaplun A, Ferrando D, et al. INVESTIGATING THE REPRODUCTIVE POTENTIAL OF NON-MOSAIC SEGMENTAL ANEUPLOIDY: A DOUBLE-BLINDED, MULTICENTER NON-SELECTION STUDY OF 176 SINGLE FROZEN EMBRYO TRANSFERS. Abstract. Presented at: ASRM 2025 Scientific Congress. San Antonio, Texas. October 25-29, 2025.