Dados do Trabalho

Title

Cycles with mosaic embryos: what can we learn?

Objective

Advances in preimplantation genetic diagnosis techniques have allowed the detection of mosaic embryos. However, little is known about the factors influencing the occurrence of mosaicism in assisted reproduction cycles. Therefore, the objective of this study was to evaluate clinical and laboratory characteristics of cycles with mosaic embryo diagnosis through preimplantation genetic test for aneuploidies (PGT-A), comparing low-level and high-level mosaicism.

Methods

This retrospective study included all PGT-A cycles with embryos diagnosed as mosaic between January 2021 and March 2023 at Nilo Frantz Reproductive Medicine. Maternal and paternal age, fertilization rate, total and top-quality (BL1) blastocyst rate, as well as euploid (< 30% of aneuploid cells), aneuploid (> 70%) and mosaic (low-level: 30-50%; high-level: 50-70%) diagnosis were evaluated. In addition, two research groups (low-level mosaicism – LLM, and high-level mosaicism – HLM) were compared regarding blastocyst morphology (BL1 – AA, AB, or BA; BL2 – BB; and BL3 – AC, CA, BC, CB, or CC), blastocyst day (D5, D6, and D7), aneuploidy type (monosomy or trisomy), and chromosome type in mosaicism according to Denver classification (A - 156-249Mb; B - 102-145Mb; and C - 51-80Mb). Statistical analyses were performed in GraphPad Prism software (v. 6.01) through unpaired T test and Fisher’s exact test, considering P-values < 0.05 statistically significant.

Results

Between the period analyzed, 67 blastocysts were diagnosed as mosaic embryos, corresponding to 4.6% of all embryos analyzed and 12.8% of all PGT-A cycles. Regarding the cycles with embryos diagnosed as mosaic, the mean maternal age was 35.02 and paternal age 38.9 years, the fertilization, total blastocyst, and top-quality blastocyst rates were 84.4%, 66.8%, and 44.8%, respectively; it was also observed that the euploid (30.3%), aneuploid (34.8%) and mosaic rates (34.9%) were similar in these cycles. Comparing LLM (n = 47) and HLM (n = 20) groups, no statistically significant differences were observed between maternal and paternal age, body mass index, anti-müllerian hormone, oocyte maturity rate, fertilization rate, morphology and day of the blastocyst, as well as chromosome type involved in mosaicism. However, it was demonstrated a higher proportion of monosomy mosaicism in HLM in comparison to LLM (60% and 29.79%, p = 0.0289).

Conclusion

The present study characterized cycles with embryos diagnosed as mosaic and demonstrated that except for aneuploidy type, no differences were observed between LLM and HLM groups. More studies with larger sample size are necessary to confirm these findings and to understand the relation between HLM and monosomy.

Keywords

preimplantation genetic test; mosaicism; blastocyst; low-level mosaicism; high-level mosaicism.