By Laura Garrido BSc, MSc (embryologist).
Last Update: 05/30/2014

Assisted hatching (AHA) is a procedure which consists of performing a small hole in the zona pellucida (ZP) (membrane surrounding the plasma membrane of the embryo). Its aim is to enable the inner cell mass (ICM) of the embryo to break through the ZP when the embryo is at blastocyst stage so that it can implant into the maternal uterus.

In a natural manner, the embryo’s zona pellucida gradually becomes thinner. On day 6, the embryo becomes detached from the ZP in order to adhere to the endometrium and, therefore, implant into it.

There are some eggs with thickened zona pellucida, which may make it difficult for the embryo to break through and implant. These embryos have, thus, fewer chances for implantation and continue its development.

Assisted hatching

Performing this technique may increase the chances for implantation of these embryos. Assisted hatching can be made during an in vitro fertilisation or ICSI cycle, although it will raise the price of the whole process.


  • Eggs with thickened ZP
  • Embryo transfer after thawing
  • Women older than 37 with problems to become pregnant
  • High levels of basal serum FSH
  • Repeated IVF cycles failure
  • Slow embryonic growth
  • Embryos with an abnormal colour of the ZP
  • Embryos with a high cleavage rate

Should you need further information, please have a look at this article: “Indications for assisted hatching“.

Zona pellucida (ZP)


Generally speaking, we can conclude that this technique increases the embryo’s implantation rate. Nevertheless, importance should be given to the fact that the results may be very variable, since, depending on the assisted reproduction clinic, the success rate may vary greatly. This imbalance is due to the complexity of the technique and the expertise that the whole process requires.

Embryo out of the zona pellucida

Another important point that should be explained is that, if this technique is not used in those cases where it is indicated, it may not have any advantage.

Authors and contributors

 Laura Garrido
BSc, MSc
Bachelor's Degree in Biotechnology from the Pablo de Olavide University (UPO) of Seville, Spain. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI). Experience at IVF, andrology, and general analysis laboratories. Embryologist specialized in Assisted Reproduction. More information