Does laser assisted hatching of residual embryos on day 3 affect blastocyst development?

Abstract

To prospectively determine the impact of Laser Assisted Hatching (LAH) on blastocyst formation in spare, non-transferred day 3 embryos. Spare, non-transferred embryos were randomized prospectively on day 3 to LAH or non-LAH based on odd/even number designation. All hatched embryos designated for actual or possible transfer were excluded from the analysis. All spare embryos containing at least 2 blastomeres on day 3 were included. For this prospective study, the two-tailed power analysis calculation was based on a prior spare blastocyst formation rate of 35%, with a clinically relevant range deemed to be 20% to 50%. To reach 80% power with an alpha error less than 0.05, our analysis required 138 embryos in the LAH and non-LAH group. The study required approximately 12 months. Oocytes were retrieved in HTF (InVitrocareyr—IVC, Frederick, MD), hyaluronidased after 2 to 3 hours incubation and ICSI’ed one to three hours following cumulus-corona removal. Oocytes were placed in IVC-1 (IVC) after ICSI and cultured individually in this media until Day 3. Embryos were placed into CCM (Vitrolife, Denver, CO) on the morning of Day 3 for extended culture. The best embryos were identified and laser hatched prior to transfer using the Zilos laser system from Hamilton Thorne (settings: one pulse; 0.500 milliseconds duration). After transfer, all remaining odd numbered embryos were assisted hatched. Even numbered embryos were left alone. Morphologic assessment occurred on Day 2, 3, 5 and 6. Blastocysts were cryopreserved on Day 5, 6 or 7. All transfers occurred on Day 3 using a Wallace 23cm stylet (Irvine Scientific, Irvine, CA) and Cook Echotip Catheter (Cook OB/GYN, Spencer, IN) under abdominal ultrasound guidance and were performed by the same physician. In the 34 patient cycles included in this study, 67.6% resulted in pregnancy after transfer with an implantation rate of 37%. In these 34 cycles, 157 embryos were designated to the laser-hatching group and 153 were not assisted hatched. Forty-three laser-hatched embryos reached the blastocyst stage (27.4%) and were cryopreserved. Forty non-laser assisted-hatched embryos developed to blastocysts (26.1%) and were cryopreserved. Blastocyst formation rates between the two groups did not reach statistical significance. (Chi-Square, p=0.80455246). Assisted hatching of non-transferred embryos by retrospective analysis had previously shown a small, but statistically significant enhancement in blastocyst formation (Portmann et al., ASRM, 2003). The results of that study were potentially skewed by the inclusion of higher quality hatched, but non-transferred embryos. In this prospective analysis, and with better randomization, there appears to be no impact of laser hatching upon embryo development to the blastocyst stage. This finding, albeit with a relatively small number of embryos, is reassuring as assisted hatching techniques shift towards greater utilization of the laser.