ASSISTED HATCHING

WHAT IS ASSISTED HATCHING?

Assisted Hatching is a Laboratory procedure whereby the shell (zona pellucida) around the early 2-3 day old embryo is mechanically or chemically weakened in a way that assists the embryo to "hatch" from the zona more easily and allow implantation into the lining of the uterus.

Normally, the "hatching" process involves dissolving of the zona pellucida at about 120 hours (5 days) after fertilisation. This allows the embryo to leave the protected environment of the zona pellucida and commence implanting into the lining of the uterus.

Normally, the uterine lining is in a condition that is receptive for implantation for about 48 hours (i.e. from about 120 to 168 hours after fertilisation). However, in women who undergo ovarian stimulation (as occurs in IVF/GIFT etc) this window of implantation appears to be brought forward to between 72 and 120 hours after fertilisation. Thus, if hatching does not occur, or occurs after 120 hours, implantation will be unsuccessful and a pregnancy will not ensue.

The Assisted Hatching technique was commenced in 1990 by a team led by Dr Jacques Cohen at Cornell in New York. Since then a large number of reputable centres have commenced these procedures with an improvement in the subsequent implantation and pregnancy rates in a particular group of women who may benefit from this procedure.

WHO CONSIDERS ASSISTED HATCHING?

Research shows that Assisted Hatching may benefit:

• women 37 years or older or
• women with poor prognosis embryos - in some embryos (ie thick zonae, low development rate and/or excessive fragmentation) it is possible that the cellular energy level required for normal hatching may be insufficient or
• women who have had repeated (3 or more) implantation failures or
• frozen embryos which may have hardened zonae pellucidae

BENEFITS OF ASSISTED HATCHING  

There is some evidence that Assisted Hatching of embryos in selected cases (set out above) may improve the percentage of embryos that implant. Current research shows that pregnancy rates after Assisted Hatching in various units around the world have either increased in those groups that are thought to benefit from this procedure or remained unchanged. Results from research by Cohen and colleagues has shown that the implantation rate of embryos with thickened zonae that were assisted to hatch was 25% compared to 18% in embryos that did not have Assisted Hatching. In these studies the increase in implantation rate occurred without causing damage to the embryo nor increasing rates of miscarriage or birth defects.

Other research shows that no differences in the rate of birth defects were observed in babies born from embryos that were assisted to "hatch" (2.4%) compared with those did not have Assisted Hatching (2.6%).

DISADVANTAGES OF ASSISTED HATCHING

In some instances, the creation of a weakness in the zona pellucida will not be enough to improve the chances of the embryo to adequately hatch.

Current research shows that the benefits of Assisted Hatching are limited to selected cases and there is no evidence of benefit for the overall patient population.

Although some centres around the world report no changes in the rate of multiple pregnancy following Assisted Hatching, research from other centres suggests that there may be an increase in multiple pregnancy following Assisted Hatching. One study has shown that although Assisted Hatching did not increase the multiple pregnancy rate, it was associated with a 2-fold increase in monozygotic twins (identical). It is therefore important to carefully consider the number of embryos assisted to "hatch" and the potential risks associated with multiple pregnancy, particulary monozygotic twinning. These issues should be discussed with your Gynaecologist.

Assisted Hatching procedure can only be performed in association with IVF/ICSI. (see IVF/ICSI Information Sheets).

MANAGEMENT OF ASSISTED HATCHING

Usually up to 2 embryos (3 in exceptional circumstances) may be assisted to "hatch". This can only be performed on embryos with at least 6 cells, so replacement of embryos will usually be undertaken 3 days after egg collection.