Impact of different types of embryonic mosaicism on pregnancy outcomes

Mosaic embryos can yield healthy live births, although pregnancy outcomes are inferior to those with euploid embryos. Pregnancy outcomes also vary significantly among mosaic embryos with different characteristics, yet current classifications lack sufficient granularity to reflect this heterogeneity. However, prevailing classification systems lack sufficient granularity to adequately reflect this heterogeneity. The objective of this study is to delineate pregnancy outcome differences among mosaic embryos categorized using a refined classification framework that provides greater resolution of mosaicism characteristics.

A retrospective study comparing the pregnancy outcomes of embryo transfer cycles transferring euploid and mosaic embryos.

A total of 434 cycles of mosaic embryo transfers and 868 cycles of euploid embryo transfers were included.

The euploid or mosaic embryos transferred and the characteristics of mosaicism.

Clinical pregnancy rate, ongoing pregnancy rate, live birth rate, first-trimester pregnancy loss rate, incidence of maternal complications, and congenital anomalies.

Generalized estimating equation (GEE) models were used to compare pregnancy outcomes between groups. Overall, mosaic embryos were associated with significantly inferior pregnancy outcomes than euploid embryos, driven primarily by high-level mosaic embryos. Compared with euploid embryos, the segmental mosaic embryos had similar pregnancy outcomes, whereas the chromosomal mosaic embryos had worse pregnancy outcomes, with lower clinical pregnancy rate (odds ratio [OR]=0.65; 95% confidence interval [CI]: 0.43-0.98), ongoing pregnancy rate (OR=0.56; 95%CI: 0.37-0.84), and live birth rate (OR=0.61; 95%CI: 0.41-0.92). Within chromosomal mosaic embryos, pregnancy outcomes did not differ significantly between monosomy mosaic and euploid embryos. In contrast, chromosomal trisomy mosaic embryos presented markedly worse outcomes than euploid embryos across all measures: biochemical pregnancy rate (OR=0.46; 95%CI: 0.25-0.83), clinical pregnancy rate (OR=0.48; 95%CI: 0.27-0.84), first-trimester pregnancy loss rate (OR=6.00; 95%CI: 1.99-18.11), ongoing pregnancy rate (OR=0.32; 95%CI: 0.18-0.58), and live birth rate (OR=0.35; 95%CI: 0.19-0.63). Finally, the incidence of maternal complications and congenital anomalies did not differ significantly between mosaic and euploid groups.

Segmental and chromosomal monosomy mosaic embryos have pregnancy outcomes comparable with those of euploid embryos, whereas chromosomal trisomy mosaic embryos are associated with significantly poorer outcomes.