The assisted hatching procedure involves thinning or making a small hole in the zona pellucida that surrounds the embryo (a protective layer). Some studies suggest that assisted hatching may improve implantation rates. Before an embryo implants into the uterus, it must “hatch” from the zona pellucida. There is some evidence that in some women, the zona may be thickened or hard, restricting the embryo from hatching.  Thus, by making a small hole in the zona pellucida, the hatching can occur without issue.
Just before the embryos are transferred back to the patient, a small hole is made in the zona pellucida. The process is performed on each embryo that is to be transferred. The hatched embryos are then transferred into the uterine cavity as usual Techniques used for assisted hatching include chemical (acid), mechanical, and laser. Damaging embryos from this procedure is extremely rare.

Assisted hatching of a day three embryo. 
The embryo is in the center and is being hatched on the right. 
A small pipette is used to make a small hole in the embryo’s shell
(the zona pellucida) to enhance embryo implantation.

The success rate associated with assisted hatching varies widely between clinics. This could be due to differences in
their patient populations, experience, and the technique used for assisted hatching. Some clinics reported no benefit when assisted hatching was offered to all patients, while others reported significant increases in clinical pregnancy and implantation rates following assisted hatching when the procedure was performed in selected groups of patients.
Which patients are optimal candidates for assisted hatching?

• Women over 37 years undergoing IVF
• Women experiencing recurrent implantation failure (three or more embryo transfers without a pregnancy)
• Women whose embryos exhibit a thick zona pellucida
• Women with elevated FSH levels
• Women with unexplained infertility