Abstract: Objective: To investigate the effects of laser-assisted hatching （LAH） on clinical outcomes of vitrified-warmed embryo transfer at the cleavage stage and blastocyst. Methods：565 vitrification-frozen embryo transfer（FET） cycles were retrospectively studied. According to whether the AH was performed, 426 cleavage stage embryo transfer cycles were divided into two groups: AH group and non-AH group; 139 blastocyst transfer cycles were divided into two groups: AH1 group and non-AH1 group. The general condition and pregnancy outcome were compared. Results：There were not significant differences in clinical pregnancy rate, implantation rate, multi-pregnancy rate, miscarriage rate and ectopic pregnancy rate between the AH group and the non-AH group （P＞0.05）. The implantation rate and multi-pregnancy rate in the AH1 group were significantly higher than those in the non-AH1 group （P＜0.05）. There were not significant differences in the rates of clinical pregnancy, miscarriage and ectopic pregnancy between the AH1 group and the non-AH1 group （P＞0.05）. Conclusions：LAH can increase the rates of implantation and multi-pregnancy in vitrified-warmed blastocyst transfer, but it does not increase the clinical pregnancy and implantation rates of vitrified-warmed embryos transfer at the cleavage stage.

Key words: Cleavage stage, ovum, Embryo transfer, Blastula, Laser therapy, Pregnancy outcome