Frequencies of chromosome-specific mosaicisms in trophoectoderm biopsies detected by next-generation sequencing

Objective: To examine the chromosome-specific frequencies of mosaicism detected by next-generation sequencing (NGS) compared with constitutional aneuploidy. Design: Retrospective cross-sectional review of NGS results from trophectoderm biopsies analyzed by per-chromosome prevalence of mosaicism and constitutional aneuploidy. Setting: Private fertility clinic. Patient(s): A total of 378 patients who underwent preimplantation genetic screening by NGS for routine clinical indications from February 2016 to April 2017. Intervention(s): None. Main Outcome Measure(s): Aneuploidies and mosaicisms were tabulated per chromosome, and whole-chromosome and segmental mosaicisms were also analyzed. Result(s): NGS results were analyzed from 1,547 blastocysts. Mosaicism was detected as the sole abnormality in 17.5% (n = 270) of samples but were also found in 196/634 aneuploid embryos, so the overall incidence of mosaicism per biopsy was 30.1%. Mosaicism did not statistically vary when stratified by maternal age. The mean rate of overall mosaicism per chromosome was 2.46%. When whole chromosome and segmental mosaicisms were compared, unequal frequencies were found in several chromosomes. Trisomy was more frequently detected as whole-chromosome mosaicism, although monosomy was more frequently seen in segmental mosaicism. Aneuploidy and mosaicism displayed different patterns of distribution in various chromosomes. Conclusion(s): Mosaicism is unequally detected in various chromosomes and appears distinct from the distribution pattern of constitutional aneuploidy. Whole chromosome and segmental mosaicisms are also differentially detected. These results contribute to the study of mosaicism, illuminating a differential pattern of detection across the genome. (C) 2018 by American Society for Reproductive Medicine.