The embryo has a thin transparent capsule that surrounds it called zona pellucida (ZP). ZP plays an important role in protecting the embryo until the blastocyst stage. Normally, the ZP will break down at the blastocyst stage to allow the inner cells of the embryo to implant in the endometrium of the uterus. In other words, before an embryo can implant into the endometrium, it must hatch out from the ZP.
There is evidence that, in some women, the ZP becomes thick and tough and this restricts the embryo to hatch. In other cases, the embryos have insufficient energy to expel themselves from the ZP. The indications of assisted hatching are those embryos with thick ZP or repeated unsuccessful IVF cycles. Assisted hatching helps by artificially making a hole in the ZP for the inner cells to hatch.
The process of assisted hatching is time-consuming and requires an advance inverted microscope, micro-manipulator, and a skillful embryologist. The embryo is held in place by a micro vacuum tip pipette. The hole in the ZP is made by the means of a mechanical, chemical, or laser (see video).
The process of assisted hatching is associated with damage to the embryos (1%), increased identical twins, and fetal malformations.