Guide to Assisted Hatching

After having undergone an IVF treatment some people are lucky enough to be told that not only do they have 2 good quality embryos to transfer back into the uterus but that they have some embryos that are of high enough quality to be frozen (approximately 50% of couples have enough embryos to freeze).  Though it is becoming quite common to perform assisted hatching on fresh embryos, it is a relatively new idea for frozen embryos to undergo the procedure.

It is actually quite difficult to get embryos suitable for freezing during a fertility treatment as the criteria for freezing is actually higher than that for a fresh transfer.  This is because as water expands on freezing, any embryo which has even a small amount of fragmentation can be split apart by the increasing size of the ice.  With a fresh embryo transfer this is not an issue and so embryos with a small amount of fragmentation can still be transferred.

All infertility treatments have varying success rates depending on a variety of factors, including maternal age, cause of infertility and expertise of the clinic performing the procedure.  However, frozen embryo transfers generally have a much lower success rate than fresh embryos transferred after IVF or ICSI.  It is thought that one of the reasons for this is that the freezing process itself thickens the zona pellicuda, making it more difficult for the embryo to hatch out after it has been thawed.

Approximately 75-85% of embryos survive thawing and so it is generally recommended to thaw 3 or 4 embryos at a time to ensure that some will survive to be put back into the woman.  The loss of embryos tends to be seen when they don’t resume their division once thawed.  Several studies have shown that by performing assisted hatching on the thawed embryos they stand a much better chance of hatching out of their protective coating.  Obviously this has the knock on effect of improving the likelihood that the embryo will implant and go on to provide a viable pregnancy.

The process of performing assisted hatching on a thawed embryo is identical to carrying out the procedure on a fresh one and the risk of damage to the embryo is also exactly the same, at about 1%.  Some people choose to have a frozen embryo transfer over a fresh transfer.  This can be for a variety of reasons.  Some advantages of a frozen embryo transfer (FET) are that there is no risk of ovarian hyper stimulation syndrome (OHSS) and if a woman falls ill or suffers uterine bleeding just before transfer, both of which would reduce the likelihood of the fresh transfer succeeding.

The most common reason for an IVF treatment to fail is because the embryos don’t implant: either because the embryos have failed to progress or due to a failure to hatch.  Assisted hatching is one procedure that aims to reduce the number of embryos which don’t hatch (either because their protective layer is too thick, or the embryo doesn’t have enough energy to break out).

Assisted Hatching was first carried out in the 1990s.  It is performed in order to help an embryo hatch out of its protective protein coat and implant into the uterus. The coat surrounds the embryos and helps to regulate fertilisation by preventing more than one sperm from penetrating the egg. It also acts as protection during the early stages of development.

Research has shown that assisted hatching is only beneficial for certain groups of patients.  Studies have shown that where it is carried out after fertility treatment for all groups of patients it doesn’t increase the chances of success.  However, when the patient is selected on specific criteria it can produce a considerable improvement in success rates.

The first group for whom assisted hatching IVF is recommended is women over the age of 37.  This is because as a woman ages, so do her eggs resulting in a thickening and hardening of the protective layer.  This is part of the reason why the IVF process becomes less successful as women age.  For this reason assisted hatching is particularly useful for older women and those whose embryos are known to have a particularly thick zona pellicuda.

The second group is those who have suffered repeated failed infertility treatments.  Though the exact causes of these failures is rarely known it has been shown that the procedure can significantly improve the chances of success for these women.

The final group is women who are found to have an elevated FSH (follicle stimulating hormone) on day 3 of their monthly cycle.  You would hope that FSH levels would be less than 15 mIU/mL on day 3 but if they are above this then it is an indicator of a failing ovarian reserve.  This happens as a woman approaches the menopause.  Having a high FSH when you are quite young is a sign that your eggs are prematurely aging, which could be the cause of your IVF failure as, just like older women, the protective layer is beginning to thicken.