Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.

Objective: To assess whether the extent of chromosomal mosaicism can influence the success rate of IVF treatments.

Design: Prospective study.

Setting: Private genetic and assisted reproduction centers.

Patient(s): The transfer of mosaic embryos was offered to 77 women for which IVF resulted in no euploid embryos available for transfer.

Intervention(s): All embryos were cultured to blastocyst stage; trophectoderm biopsy was performed on day 5/6 of development. Comprehensive chromosome screening was performed using either next-generation sequencing or array-comparative genomic hybridization methodologies.

Main Outcome Measure(s): The clinical outcome obtained after transfer of mosaic embryos with low (<50%) and high (≥50%) aneuploidy percentage was compared with that resulting from a control group of 251 euploid blastocysts.

Result(s): A significantly higher implantation rate (48.9% vs. 24.2%), clinical pregnancy rate/ET (40.9% vs. 15.2%), and live-birth rate (42.2% vs. 15.2%) were observed comparing embryos with mosaicism <50% and ≥50%. Mosaic embryos with high aneuploidy percentage (≥50%) showed a significantly lower clinical pregnancy rate/ET (15.2% vs. 46.4%), implantation rate (24.4% vs. 54.6%), and live-birth rate (15.2% vs. 46.6%) than euploid blastocysts. In contrast, embryos with lower aneuploidy percentage (<50%) have a clinical outcome similar to euploid embryos.

Conclusion(s): The results of this study further confirm that mosaic embryos can develop into healthy euploid newborns. We demonstrated that the extent of mosaicism influences the IVF success rate. Mosaic embryos with low aneuploidy percentage have higher chances of resulting in the birth of healthy babies compared with embryos with higher mosaicism levels.