A defect in the hatching stage is considered an important cause of implantation failure. Therefore, assisted hatching (AH), which involves artificial disruption of the zona pellucida, has been proposed as a method for improving the capacity of the embryo to implant. But the advantage of using laser to facilitate the hatching process of embryos in ART practice is debatable, and an optimum strategy for performing LAH remains elusive. Therefore, the aim of this study was to evaluate the effects of laser-assisted hatching(LAH) on clinical outcomes. Patients were randomly divided into control and LAH groups. The zona pellucida was thinned or drilled with a diode laser. Relevant parameters are recorded to evaluate the validity of LAH in ART.

Hatching is a very important process for successful implantation involving the breaking of the embryo out of the zona pellucida at the blastocyst stage. Inadequate hatching of the blastocyst might lead to implantation failure in ART. Currently, a variety of AH techniques have been used including zona thinning and the opening or complete removal of the zona by laser. But the advantage of using laser to facilitate the hatching process of embryos in ART practice is debatable, and an optimum strategy for performing LAH remains elusive. Therefore, the investigator aim to discuss the effectiveness of LAH in ART.

In this study, patients were randomly divided into control and LAH groups. A quarter of zona pellucida of the cleavage-stage embryo was thinned to 6.6 μm. All operation was performed in the empty region without contact to the blastomere in order to minimize the blastomere damage. The ZP of blastocyst was drilled with laser, the ZP opening 20% of its initial length. The operation was performed in the opposite region of ICM in order to minimize the damage. In the control group, embryos were transplanted without LAH. The rate of clinical pregnancy, live-birth, miscarriage, multiple gestation were evaluated. This research intends to discuss whether LAH can improve the clinical outcomes in ART, and further choice the appropriate LAH action site.

Inclusion Criteria:

• Patients undergoing IVF/ICSI-ET cycle；
• The zone pellucida of the cleavage-stage embryo is thicker than 8 μm.

Exclusion Criteria:

• Number of embryos transferred per cycle >2;
• The transferred embryos including fresh and frozen cycle in the same cycle;
• Embryos developed from the frozen-thawed oocytes.