Degree of mosaicism in trophectoderm does not predict pregnancy potential: A corrected analysis of pregnancy outcomes following transfer of mosaic embryos

Background: Preimplantation genetic screening (PGS) is increasingly utilized as an adjunct procedure to IVF. Recently healthy euploid live birth were reported following transfer of mosaic embryos. Several recent publications have surmised that the degree of trophectoderm (TE) mosaicism in transferred embryos is predictive of ongoing pregnancy and miscarriage rates. Methods: This is a corrected analysis of previously published retrospective data on vitro fertilization (IVF) cycle outcomes involving replacement of 143 mosaic and 1045 euploid embryos tested by PGS, utilizing high-resolution next-generation sequencing (NGS) of TE and determination of percentages of mosaicism. Receiver operating curves (ROCs) and measurement of area under the curve (AUC) were used to evaluated the accuracy of the predictor variable, proportion of aneuploid cells in a TE biopsy specimen, with IVF outcomes, ongoing pregnancy and miscarriage rates. Results: Confirming findings of the previously published report we also found higher ongoing pregnancy rates (63.3% vs. 39.2%) and lower miscarriage rates (10.2% vs. 24.3%) with euploid embryo transfers than with mosaic embryo transfer. There, however, were no significant differences in ongoing pregnancy or miscarriage rates among mosaic embryo transfers at any threshold of aneuploidy. Based on AUC, TE biopsies predicted ongoing pregnancy for euploid, as well as mosaic embryos, in a range of 0.50 to 0.59 and miscarriage in a range from 0.50 to 0.66 Conclusions: Degree of TE mosaicism was a poor predictor of ongoing pregnancy and miscarriage.