Another microsurgical procedure performed in the IVF laboratory is Assisted Zona Hatching (AZH). AZH is a procedure performed on all embryos prior to transfer to the uterus on Day 3 of embryo development. This is done in order to increase the chance of embryo implantation and pregnancy. Each human embryo is surrounded by a "shell" called the zona pellucida. The embryo must break out of this "shell" in order for implantation to occur. An unusually thick or hard "shell" is thought to reduce the likelihood of implantation and pregnancy. Therefore by creating an artificial opening in the "shell" the likelihood of implantation is thought to increase.

Assisted hatching is performed using micromanipulation instruments attached to a microscope. The embryo is held in position by gentle suction from a micropipette. An opening is created in the zona pellucida using fine glass needle. The needle never comes in contact with the embryo but allows for an incision to be made in the outer shell. This procedure is performed in a drop of nutrient medium and afterward the embryo is returned to culture until the embryo transfer procedure is performed. This opening is thought to facilitate hatching, which normally takes place in the uterus, and enhance contact with the lining of the uterus.

Assisted hatching is most useful for the following types of patients:

• Patients older than 38 years of age
• Patients with elevated levels of follicle stimulating hormone (FSH)
• Patients with embryos thicker than normal zona pellucida
• Patients with previous multiple IVF attempts with failed implantation