Received May 17, 2006
Accepted August 14, 2006

Introduction:The objective of the present study was to evaluate the efficacy of quarter-laser zona thinning assisted hatching(qLZT-AH) in improving the implantation rate of cryopreserved-thawed(CT) embryos. Methods:A total of 258patients who participated in and ICSI program and had their embryos cryopreserved were divided into two groups:Group I (n=220), patients who had all their supernumerary embryos cryopreserved, independently of their morphology and Group II(n=38), patients with risk of ovarian hyperstimulation syndrome(SHO) who had all their embryo cryopreserved. Patients were randomized to be included in the group where qLZT-AH was performed (experimental group) or not(control group) in both population, at the moment of embryo transfer.The population characteristics:age, number of previous transfers, etiology, infertility duration, number of embryo frozen; the embryo factors: survival, cleavage, embryo ZP thickness, embryo quality and the outcomes:implantation and pregnancy rates were evaluated.The transfers were performed by two different protocols:artificial and natural protocols. Results:Embryo implantation of the hatched embryos did not demonstrated significant difference in relation to the implantation of not hatched embryos in both patients population(GroupI:qLZT-AH=7.8%, Control=7.9; GroupII:qLZT-AH=28.8%, Control=14.2% ).The patients who frozen all their embryos(Group II) presented significant higher pregnancy and implantation rates compared to the patients who had exceeding embryos cryopreserved(Group I)(39.5% and 21.3%; 18.2% and 7.8%,respectively). Patients of the Group I who transferred intact embryos in artificial cycles showed higher pregnancy and implantation rates compared to the patients who transferred intact embryos in natural cycles (27.1% and 7.8%;12.2% and 2.9%, respectively). Conclusion:The present data shown that the qLZT-AH methodology is not efficient to improve implantation rates of cryopreserved embryos.