The effect of laser-assisted hatching on clinical outcomes of frozen-thawed embryo transfer at different embryo ages

To investigate the impact of laser-assisted hatching (LAH) on clinical outcomes in patients undergoing frozen-thawed embryo transfer (FET) cycles with embryos at different developmental stages. We conducted a retrospective analysis of 2,208 patients who underwent vitrification-thawed FET at our reproductive center between October 2018 and June 2024, with some patients contributing multiple cycles. Patients were stratified by embryonic developmental stage into cleavage-stage FET (n=793) and blastocyst-stage FET (n=1,415) groups. Each group was further subdivided based on post-thawing LAH implementation: Non-LAH and LAH subgroups (cleavage-stage: Non-LAH (n=363) vs. LAH (n=430); blastocyst-stage: Non-LAH (n=532) vs. LAH (n=883)). Embryological parameters and clinical outcomes were compared across subgroups. Binary logistic regression analysis was performed to assess the impact of LAH on live birth rates after adjusting for confounding factors. In cleavage-stage FET, LAH group had higher clinical pregnancy rate (39.3% vs 27.5%), implantation rate (25.2% vs 17.7%) and live birth rate (25.8% vs 19.8%) than Non-LAH group (P0.05). Binary logistic regression analysis showed that after adjusting for confounding factors, LAH could increase the live birth rate of patients with cleavage FET (OR=1.529, 95% CI=1.081-2.162, P=0.016). However, it had no effect on the live birth rate of FET patients at the blastocyst stage (OR=0.988, 95% CI=0.794-1.230, P=0.914). In the FET cycles, LAH can improve the live birth rate of patients undergoing cleavage-stage FET, especially for women aged ≥35 years or those with ≤2 previous transfers, but has no significant effect on the live birth rate of patients undergoing blastocyst-stage FET. LAH did not increase the risk of perinatal outcomes in either the cleavage-stage or blastocyst-stage embryo transfer.