Effect of the size of zona pellucida thinning by laser assisted hatching on clinical outcome of human frozen-thawed embryo transfers.

Of 122 consecutive procedures, 31 were not assisted hatching (AH), which served as the control group, 34 were AH with 40 microm thinning of the zona, and 57 were AH with 80 microns of the zona thinning. The pregnancy and implantation rates were significantly higher in 80 microns thinning group compared to control group (40.3 vs. 16.1 percent, P=0.03; 21.5 vs. 7.5 percent, P=0.007, respectively). In addition, the implantation rate was signigicantly higher in 80 microns group than in 40 microns group (21.5 percent vs.9.4 percent, P=0.024). The results indicated that the size of the zona pellucida thinning by laser may influence the pregnancy and implantation rates following frozen-thawed cleaved embryo transfer.