Received April 30, 1998
Accepted October 17, 1998

Introduction: "Assisted Hatching" (AR) is a technique used to improve pregnancy rates among patients ≥38 years old and/or patients presenting previous failure of implantation. The objective of the study was to determine whether AR (thinning) has a beneficial effect on patients younger than 37 years who are being submitted to the first ICSI attempt. Material and Methods: A total of 60 patients submitted to ICSI for the first time and aged ≤37 years were divided into 2 groups in a prospective and randomized manner: group I – Patients submitted to AR(n=25); a laser diode with 1.48µm wavelength was used for the procedure; group II - Patients with no AR(n=35). ln both groups, embryo transfer was performed on the 2nd day. Results:The age of group I patients(31.72±3.70) did not differ(p=0.85) from that of group II patients (31.54±3.65). The number of embryos transferred was similar(p= 0.60) for the two groups (group I=2.76±0.92;group II=2.89±0.67). The thickness of the zona pellucida of group I embryos (16.52±1.65µm) did not differ (p= 0.23) from that of group II embryos (16.87±1.77µm). The rate of embryo implantation (24.63% ) and the rate of c1inical pregnancy per embryo transfer (44%) were higher for group I than for group II(19.8% and 37.14%, respectively), but the difference was not significant (p=0.45 and p=0.60). Discussion:AR of the thinning type in patients aged ≤37 years and with no previous failure of implantation led to higher implantation and pregnancy rates than in controls, although thus far the difference has not reached significance.