The normal process of conception requires escape or “hatching” of the early embryo from the zona pellucida shell. Hatching usually occurs around the 6th or 7th day following fertilization and is required for the embryo to attach, or implant, in the uterus. Sometimes, this is observed when transferring day 5 embryos but many times it does not happen until after a transfer has occurred. Inability of the embryo to complete the hatching process may interfere with implantation. Assisted hatching is a laboratory procedure designed to reduce the chance that an embryo will be unable to proceed beyond this stage. Some studies suggest that IVF pregnancy rates are improved if assisted hatching is performed on the 3rd day of embryo development, particularly in older women. This is accomplished by creating a small hole in the zona pellucida by the energy from a focused laser beam.
The ART program may recommend assisted hatching in select circumstances that include advanced maternal age or previous IVF failure. Assisted hatching is also performed routinely in PGS/PGD cases in order to make the embryo biopsy easier, and in many frozen embryo transfers.