Received April 30, 1998
Accepted October 17, 1998

Introduction: The implantation and pregnancy rates obtained after the transfer of cryopreserved embryos are usually lower than those obtained after the transfer of fresh embryos. The objective of the present study was to determine the rates of implantation and pregnancy after the u s e of laser for "Assisted Hatching" (AH) in cryopreserved embryos after ICSI. Material and Methods:A total of 48 patients presented thawed embryos from April to October 1998 and at least 1 embryo cleaved after thawing and culture for 24 hours. A laser diode with 1.48µm wavelength (Fertilaser) was used for the AH procedure. A single opening of about 15µm was made in the zona pellucida at the time of embryo transfer. Results:Patient age was 31.75± 4.43 years and the mean number of thawed embryos was 6.62±3.60. Embryo survival was 76.44 ± 26.58%, and the number of transferred embryos was 3.4±1.36. The mean thickness of the zona pellucida in the population of thawed embryos (18.17±2.21µm) was significantly greater (p=0.02) than the mean thickness (16.5±1.4µm) of the control group (age:31±3.6 years, with no failure implantation). The rate of embryo implantation was 8% (13/163), the pregnancy rate per transfer was 22.9%(11/48) and the abortion rate was 9.09%(1/11). Discussion:The thickness of the zona pellucida of cryopreserved embryos is increased. The embryo implantation and pregnancy rates obtained after AH with laser may present benefits in a cryopreservation program