Sometimes egg shell is thicker than 15 micrometers (a unit of measurement under a microscope, for tiny objects that are not visible to the naked eye). Embryos cannot hatch through and unable to implant in the uterus causing failed pregnancy rate. Assisted hatching by thinning the shell or piercing a hole helps embryo hatch and implant in the uterus. The use of laser to penetrate egg shell is called LAH or Laser Assisted Hatching. Laser is precise, no harm to the embryo, and increase pregnancy chance.