The outer layer of an embryo is known as the zona pellucida (or zona). When the embryo is about 5 or 6 days old, it needs to escape (or hatch) from the zona pellucida in order to implant in the womb.

Some patients may produce embryos in which the zona is thickened or becomes hardened. This thickening or hardening of the zona may prevent the embryo from hatching and implanting.

Several factors may cause this problem, namely, an elevated FSH level, increasing age of the female partner and the manipulation of the egg during the technique known as intracytoplasmic sperm injection (ICSI). We would also recommend that patients who have had three unsuccessful embryo replacements consider assisted hatching.

Assisted hatching is a technique whereby a small artificial gap is created in the zona. The gap is created by gently blowing an acid solution at a small area of the zona (see pictures below). It is thought that the embryo can then hatch more easily through this gap, and hopefully increase the probability of implantation. The assisted hatching procedure is performed just before embryo replacement.

The benefits and risks of assisted hatching are as yet unproven, and it should still be considered an ‘experimental’ procedure.


Pictures of Assisted Hatching taking place

   

Embryo gently held in place                   Zona starts to dissolve as acid is blown at it

    

Zona dissolves further                          Hole visable in zona