Abstract
Recently, reports showed that embryos identified as mosaic after preimplantation genetic testing for aneuploid (PGT-A) could result in live birth with lower pregnancy and higher pregnancy loss rates compared with euploid embryos. However, the effects of mosaicism level on reproductive outcomes remain controversial. This study aimed to examine the level of mosaicism on pregnancy outcomes. Single mosaic embryo transfer was offered to 108 women who only had mosaic embryos. Mosaic embryos were labeled by utilizing next generation sequencing (NGS) based PGT-A for day 5/6 trophectoderm (TE) biopsies. TE biopsies containing < 50% abnormal cells were classified as low-level mosaicism and ≥ 50% as high-level mosaicism. To further confirm the concordance of chromosome constitution between TE and inner cell mass (ICM), 41 remaining embryos designated as mosaic blastocysts donated for research were also analyzed. Comparable live birth rate (LBR) but higher miscarriage rate (MR) was found in the high-level group. (LBR: low vs. high: 44.5% vs. 36%; p = 0.45, MR: low vs. high: 5.1% vs. 30.7%; p = 0.012). Analyses of TE and ICM from the remaining mosaic blastocysts show a poor concordance. This preliminary study demonstrated that high-level mosaic embryos could result in comparable LBR but higher MR.
Highlights
Preimplantation genetic testing for aneuploidy (PGT-A) aims to improve in vitro fertilization (IVF) outcomes by avoiding aneuploidy embryo transfer
The findings of this study are valuable for understanding the clinical results after single embryo transfer (SET) with low/high level mosaic embryos
The present study demonstrates that high-level mosaic embryo transfer resulted in a comparable live birth rate (LBR), but higher miscarriage rate (MR) compared with low-level mosaic embryos
Summary
Preimplantation genetic testing for aneuploidy (PGT-A) aims to improve in vitro fertilization (IVF) outcomes by avoiding aneuploidy embryo transfer. Compared with other methods for PGT-A, higher-resolution next-generation sequencing (hr-NGS) has higher chromosomal analysis resolution and is capable of detecting mosaicism levels as low as 20% [1]. Published data suggest that mosaic embryos result in a live birth, but with a lower pregnancy rate and a higher pregnancy loss rate compared with euploidy embryos [4,5,6,7,8,9,10]. Considerable uncertainty remains regarding the relation with clinical outcomes, type and level of mosaicism, and the number of chromosomes involved, and clarification of these issues is needed before prioritizing mosaic embryos. Current follow-up data obtained after mosaic embryo transfer is still insufficient to draw any conclusion related to which mosaicism should be prioritized for transfer
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