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Assisted hatching

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How does assisted hatching work?

Before an embryo can attach to the wall of the womb, it has to break out or ‘hatch’ from its outer layer, the zona pellucida. It has been suggested that making a hole in, or thinning, this outer layer may help embryos to hatch, which may increase the chances of pregnancy.

However, assisted hatching does not improve the quality of embryos.

The NHS guidelines on fertility, issued by NICE (the National Institute for Health and Clinical Excellence), say:

‘Assisted hatching is not recommended because it has not been shown to improve pregnancy rates.’ 

The guidelines also mention that further research is needed to find out whether assisted hatching can have an effect on live birth rates and to examine the consequences for children born as a result of this procedure.

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What is assisted hatching?

Assisted hatching is done while the embryo is in the laboratory.

Before being transferred back to the womb a hole is made in the outer layer of the embryo or it is thinned, using acid, laser or mechanical methods.

A typical procedure is:

Step 1. On day three of embryo development, the embryologist uses either weak acid in a fine glass pipette, a microlaser or a microtool to thin or cut a hole in the outer layer of the embryo.

Step 2. If weak acid was used, the embryo is washed to prevent further damage.

Step 3. Because assisted hatching thins or makes a hole in the protective outer layer around the embryo, the woman may be given antibiotics to prevent infection.

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What is my chance of having a baby with assisted hatching?

Some clinicians believe that the use of assisted hatching results in higher pregnancy rates in selected cases.  For example, it has been noted that in the older woman the zona pellucida around the embryo can appear to be thickened. The making of a ‘weak point’ in the zona may help implantation.

Others feel that there is no convincing evidence that it helps to improve chances of pregnancy.

If your clinic suggests this treatment, talk it through with them, asking why they are recommending it and what the benefits will be. You should also ask for any written information they may have on this treatment.

Female fertility diminishes with age, so if you are using your own eggs, on average, the younger you are, the higher your chances of success.

In the year from 01/01/2008 - 31/12/2008, for women receiving assisted hatching with stimulated IVF or ICSI using fresh embryos created with their own eggs, the percentage of cycles started that resulted in a live birth is:

  • 29.2% (92/315) for women aged under 35
  • 24.1% (53/220) for women aged between 35-37
  • 25.5% (70/274) for women aged between 38-39
  • 16.9% (51/302) for women aged between 40-42
  • 5.6% (4/72) for women aged between 43-44
  • **(0/9) for women aged over 44

** Percentages are not calculated where there are less than 50 cycles. Figures given in brackets are (cycles resulting in a live birth / all cycles started).

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What are the risks of assisted hatching?

Current research suggests that this treatment is no more likely to cause an abnormality to the baby than IVF without assisted hatching. As it is only the outer layer that is affected by this procedure, the embryo should remain unharmed.


There is always some risk of damage with any procedure of this type.


If you have more than one embryo transferred, this may increase the risk of multiple births.


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Page last updated: 25 November 2016

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