The zona pellucida (ZP) of human eggs and embryos is an outer acellular layer with different roles during fertilization and embryo development. The main function of the ZP after fertilization is the protection of the embryo against hostile uterine factors and the maintenance of its integrity during the migration through the reproductive tract. However, once the embryo reaches the uterus it must get out of the ZP (hatching) in order to attach to the womb. In some cases, after fertilization zona pellucida becomes unusually hard, thus inhibiting embryo hatching and reducing the chances of implantation.
Assisted hatching is therefore a procedure in which the outer layer of the embryo is either thinned or opened in order to facilitate hatching. However, it is important to mention that even though assisted hatching may enhance pregnancy rate, some embryos might be damaged as a result of these interventions. Therefore, it is not recommended as a first line of treatment. In general it is preferred for women above the age of 40 and in patients with repeated implantation failures in IVF cycles.
The procedure of Assisted Hatching
There are many known methods used for assisted hatching. One procedure entails the opening of a small hole to the outer layer of the embryo, using laser technology. It is important that the hole created in the ZP is large enough to avoid trapping of the embryo during hatching, but not so large that it allows blastomere loss. Another method involves the thinning of the zona, using special enzymes, without complete lysis and perforation. Both procedures are performed in the lab by the embryologists using special equipment, for embryo manipulation, under the control of high-powered microscopes. Assisted hatching is performed separately for each embryo.
What Other New IVF Technique Might Interest You?
- In vitro maturation (IVM)
- Personal Egg Banking (Elective Oocyte Cryopreservation)
- Preimplantation Genetic Diagnosis (PGD) plus MicroSort®
- Intra-cytoplasmic sperm injection (ICSI)
- Microfertilization - IMSI
- Avoiding sickle-cell anemia
- Zona pellucida measurement
- Assessment of Embryo Reproductive Potential (ERP)