The human embryo is, like the chicken egg, surrounded by a "shell". For many years there has been speculations that this "shell", the zona, might be too hard or too thick to allow the embryo to attach to the endometrial wall.

In our own work we have found, in certain situations, that this attachment can be facilitated by thinning of the zona just before replacement of the embryo. Since a couple of years we use this technique, in some patients, where we have indications of an attachment problem. The results this far is very promising.