Whether embryos are transferred on Day 3 or 5, for implantation and therefore pregnancy to occur, the embryos have to "hatch" out of the zona pellucida (embryo shell) so that the cells of the embryos can come into direct contact with the cells lining the womb. Some studies have suggested that a possible reason for the failure of embryos to implant following IVF treatment may be the inability of embryos to undergo this hatching process.
It is possible to assist this hatching process in the laboratory by using a laser to make a small hole in the shell of the embryo. This process is known as assisted hatching.
There is no evidence of benefit in the routine use of assisted hatching in every cycle and in view of the theoretical risk (<1%) of damage during the procedure it may only be suggested in select cases:
- couples whose embryos are noted to have thickening of the zona by or highly experienced embryological team.
- couples with a history of recurrent implantation failure
- couples with an advanced maternal age.