Distinct Morphokinetic Signature of Human Embryos with Chromosomal Mosaicism

This study aimed to determine whether chromosomal mosaicism in blastocysts is associated with a distinct morphokinetic signature.

Preimplantation genetic testing for aneuploidy (PGT-A) was performed on 182 human embryos via trophectoderm biopsy on day 5 and analyzed by next-generation sequencing. Embryos were classified as euploid (n = 55), mosaic (n = 39: 21 low-grade, 18 high-grade), or aneuploid (n = 88), of which 18 with concurrent mosaicism. Prior to biopsy, embryos were cultured in a time-lapse system (EmbryoScope), and 12 morphokinetic parameters were assessed, including pronuclei fading (tPNf), cleavage times (t2-t9), morula formation (tM), blastulation start (tSB), and full blastocyst formation (tB). These parameters were compared according to ploidy status.

Patients with euploid and mosaic embryos were comparable in terms of maternal age, ART indication and embryo quality (p > 0.05). In contrast, aneuploid embryos were obtained from older patients and had lower morphological grades. Mosaic embryos showed delayed tPNf (24.8 ± 6.5 vs. 22.8 ± 2.3 h, p = 0.03) and t2 (27.6 ± 6.6 vs. 25.4 ± 2.5 h, p = 0.02) compared to euploid embryos, mainly attributable to low-grade mosaic embryos. Whole-chromosome mosaicism, but not segmental mosaicism, was associated with delayed embryo development at several intermediate cleavage time points (t3, t4, t6, t7 and t9). Aneuploid embryos showed significant delays at later stages versus euploid embryos, particularly aneuploid embryos with mosaicism at t7 (56.6 ± 8.3 vs. 52 ± 5.6 h, p = 0.02), t8 (59.1 ± 9.6 vs. 54.8 ± 6.7 h, p = 0.04), tM (90.3 ± 7.7 vs. 83.6 ± 8.2 h, p = 0.006) and tB (113.0 ± 11.6 vs. 106.6 ± 8.9 h, p = 0.03).

Mosaic embryos exhibit delays in early development (tPNf, t2) but reach later morphokinetic milestones at rates similar to euploid embryos. In contrast, aneuploid embryos, especially those with mosaicism, exhibit marked developmental delays at later stages (t7, t8, tM, tB).