Timing of assisted hatching and blastocyst euploidy: A prospective PGT-A study

Objective: To investigate whether the timing of assisted hatching (AH) independently influences blastocyst euploidy after adjustment for maternal age and blastocyst morphology. Methods: A prospective study was conducted on embryos undergoing preimplantation genetic testing for aneuploidy (PGT-A) biopsy. PGT-A was performed using paired-end next-generation sequencing and PGT-A outcomes were analyzed both as binary (euploid vs non-euploid) and as three distinct categories (euploid, mosaic, and aneuploid). Results: A total of 612 embryos were included, comprising 301 embryos with day-3 assisted hatching and 311 embryos with day-5 assisted hatching. In binary analysis, the euploidy rate was higher in the day-5 group than in the day-3 group (32.5% vs 24.3%; crude OR =1.50, 95% CI : 1.05-2.14). However, when chromosomal outcomes were categorized into three groups (euploid, mosaic, and aneuploid), no statistically significant difference was observed between groups ( P =0.08). Mosaic rates (36.5% vs 33.1%, P =0.37) and aneuploidy rates (39.2% vs 34.4%, P =0.22) were also comparable. In multivariable analysis, assisted hatching timing was not independently associated with euploidy (adjusted OR =1.36; 95% CI: 0.92-1.97). Good blastocyst morphology (adjusted OR =2.48) and maternal age ≥35 years (adjusted OR =0.53) were identified as independent predictors. Conclusion: These findings indicate that assisted hatching timing does not independently affect embryo chromosomal status, including mosaicism and aneuploidy, while maternal age and blastocyst morphology remain the primary determinants of blastocyst euploidy.