Which type of chromosomal mosaicism is compatible for embryo transfer: a systematical review and meta-analysis

Purpose Chromosomal mosaicism becomes a common phenomenon in Preimplantaion genetic testing (PGT). This meta-analysis was conducted to study which feature of chromosomal mosaicism was compatible for embryo transfer. Methods After searching the database PubMed, Embase, CCTR and related reviews up until May 2021. Two reviewers extracted relevant information and assessed study quality by the Newcastle–Ottawa scale independently. Summary Odd Radios (OR) were calculated using fixed- or random-effects models for clinical outcomes. A network meta-analysis compared the clinical outcomes of different chromosomes. Results A total of six studies with 1,106 cycles of single mosaic embryo transferred were included. Significant results of implantation rate (IR), miscarriage rate (MR), and ongoing pregnancy/live birth rate (OP/LBR) were observed when comparing embryos with mosaicism level < 50% and ≥ 50% [OR 1.42, 95% CI (1.06, 1.89); OR 0.45, 95% CI (0.27, 0.75); OR 1.74, 95% CI (1.28, 2.37)], and embryos with mosaicism with only affecting segmental chromosome(s) and only involving whole chromosome(s) [OR 1.31, 95% CI (1.01, 1.71); OR 0.57, 95% CI (0.36, 0.93); OR 1.51, 95% CI (1.15, 2.00)]. Embryos with only mosaic gains or losses had significant higher IR and OP/LBR than complex mosaicism [Gains vs complex: OR 1.75, 95% CI (1.20, 2.54); OR 1.73, 95% CI (1.16, 2.58). Losses vs complex: OR 1.90, 95% CI (1.34, 2.71); OR 2.10, 95% CI (1.44, 3.07)]. Mosaic embryos with only one chromosome involved had significant favorable outcomes of IR and OP/LBR than with three or more chromosomes involved [OR 1.76, 95% CI (1.23, 2.52); OR 1.86, 95% CI (1.25,2.78)]. Chr. 7, Chr. 2, Chr. 1, Chr. 18, Chr. 11, Chr. X, Chr. 13, Chr. 14, Chr. 12, and Chr. 9 were considered as prioritized chromosomes of mosaic embryos for transfer. Conclusions This analysis support the embryos with mosaicism level ≥ 50%, whole chromosome(s) involved, multiple mosaic abnormalities were associated with worse pregnancy outcomes. Mosaicism level of 50% could be used as a threshold to assess the mosaic embryos.