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IVF techniques

Provides information on assisted hatching, a technique to improve the implantation rate.

Assisted hatching

The assisted hatching procedure involves thinning or making a small hole in the zona pellucida that surrounds the embryo (a protective layer). There some evidence that assisted hatching may improve implantation rate. Before an embryo implant into the uterus it must hatch from the zona pellucida. There is some evidence that in some women the zona becomes toughened, restricting the embryo to hatch. Making a small hole in the zona, or by thinning it using a micromanipulation, this may make it easier for hatching to occur. Assisted hatching was first described by Cohen et al in 1988.

A hatched blastocyst seen through a microscope.

How is assisted hatching is performed?

Just before the embryos are replaced, whether they are fresh or frozen/thawed, a small hole is made in the zona, or by thinning it using a micromanipulation technique. The process is repeated for each embryo. The main methods currently in use for assisted hatching are: chemical, mechanical and laser. The process will damage about 1% of embryos.

Most IVF clinics will not perform assisted hatching if there is one embryo available because of possible damage to this embryo would result in no embryo transfer. The assisted hatched embryos are then transferred into the uterine cavity as usual. Some clinics will give the woman a course of antibiotics to prevent infection. (Assisted hatching deprives the embryo of its intact protective coat, which shields it from exposure to any harmful factors in the uterus). Assisted hatching has been implicated in an increased rate of monozygotic twins.

Success rates after assisted hatching

The success rate of assisted hatching varies widely between different clinics. This could be due to differences in their patient populations, experienced 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.

To whom assisted hatching may be advised?

  • Women over 39 years and using their own eggs.
  • Women who had recurrent failure of embryo implantation (three or more embryo transfers without a pregnancy).
  • Women whose embryos exhibit thick zona pellucida.
  • Women with elevated FSH levels.