Laser-assisted hatching of cleavage-stage embryos impairs developmental potential and increases DNA damage in blastocysts.

This study aims to investigate the influence of two- (day 2) and six-to-eight-cell-stage (day 3) laser-assisted hatchings on the developmental potential and genetic integrity of the embryos. In this prospective experimental study, two- and six-to-eight-cell-stage mouse embryos were subjected to laser hatching using 1,480 nm diode laser, and then assessed for the developmental potential and DNA integrity in blastocysts. Similarly, four-cell-stage human embryos from 20 patients were also subjected to laser hatching, and then assessed for the developmental competence. Laser-assisted hatching in mouse embryos significantly enhanced the blastocyst hatching potential on day 4.5 (P < 0.0001). However, a significant decline in blastocyst total cell number (TCN) was observed in six-to-eight-cell-stage laser-hatched embryos (P < 0.001). Conversely, no significant difference in TCN was observed between laser-hatched and unhatched human four-cell-stage embryos after 24 h. Attempt to understand the genetic integrity in laser-hatched mouse blastocysts revealed significantly higher labeling index when hatching was done at two- (P < 0.01) and six-to-eight-cell stage (P < 0.05). DNA damage induced by the laser manipulation may affect implantation and postimplantation developmental potential of the embryos. However, further studies are required to elucidate the impact of laser-induced DNA damage on the reproductive outcome.