Assisted Hatching

INTRODUCTION

Mature oocytes (eggs) are surrounded by a glycoprotein coat or shell called the zona pellucida (zona). This coat continues to surround the fertilised egg and embryo until it reaches the blastocyst stage of development (day five to six post fertilization). This is the stage at which the embryo prepares to implant in the endometrial lining of the uterus. However, before it can do this, it must break out or ‘hatch’ out of the surrounding zona.

In normal circumstances, the process of ‘hatching’ takes place through the expansion/ contraction of the blastocyst within the zona, until the zona thins and ruptures, allowing the blastocyst to escape or ‘hatch’. The embryo cannot implant, and a pregnancy will not be established, if hatching does not occur. It is possible therefore that this is a factor contributing to why some women do not become pregnant following natural conception and/or IVF.

Hatching may not occur for example if there are abnormalities in the zona pellucida. In older women and those with decreased ovarian reserve the zona may be ‘tougher’ or thicker than normal and this may prevent hatching. It is also possible that some of the laboratory processes involved in IVF may themselves result in an artificial ‘hardening’ of the zona pellucida. In IVF for example, embryos are not exposed to enzymes present in the fluid of the fallopian tube that may ‘soften’ the zona to allow hatching to occur.

ASSISTED HATCHING

Assisted hatching is a procedure carried out on embryos during an IVF cycle to help ensure that hatching can take place. A hole is made in the zona pellucida by the embryologist, using very precise micromanipulation techniques. The hole provides a weakness that will help the zona to rupture when the blastocyst begins to expand. Assisted hatching is generally performed on the day of embryo transfer (day two to five).

METHODS OF ASSISTED HATCHING

– Chemical
This involves the use of a chemical (acid tyrodes) to dissolve a weakness in the zona. This is a technically difficult procedure Ð it can be difficult to quantify and consistently reproduce the amount of chemical to which the embryo is exposed. Excessive exposure can be detrimental to the embryo.

– Mechanical
This is a micromanipulation procedure that involves the use of a microtool similar to an ICSI needle to rub a narrow slit in the zona pellucida. No chemicals are involved but it requires the skill of experienced embryologists to perform the procedure without compromising the embryo.

– Laser
This involves the use of a micro laser system to drill a precise incision in the zona. The power of the laser is predetermined by its programing, and there is a high degree of reproducibility. The process is also fast compared to the chemical and mechanical methods.

ARE THERE ANY RISKS ASSOCIATED WITH ASSISTED HATCHING?

There is some data suggesting a link between assisted hatching and identical twinning, but this evidence is inconclusive. Overall, to date, there is no evidence that assisted hatching has any other significant risks.

WHO IS SUITABLE FOR LASER ASSISTED HATCHING?

At Life Fertility Clinic the morphology of the zona pellucida and the development of embryos are observed and assisted hatching is commonly performed on an ‘as required’ basis. There are however some groups of patients that studies suggest might specifically benefit from the use of the technique. These include:

  • Those patients who are over 37 years of age.
  • Patients having a frozen embryo transfer.
  • Patients who have had a previous failed IVF or ICSI treatment cycle.
  • Patients who are considered poor responders because they have had a high dose of gonadotrophins for poor ovarian response.
  • Patients with three or fewer embryos.

 


 

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