IVF experts like me spend a lot of time trying to figure out ways to get an embryo to implant
into the uterus. One technique that has been used for many years is called assisted hatching. I have
gotten many requests from viewers to dedicate an episode of InfertilityTV to assisted hatching.
I resisted this for a long time. To find out why, stay tuned.
First a little background. An embryo is surrounded by a hard shell called the zona pellucida. It is
often referred to as just the zona. Before an embryo can implant in the uterine lining,
the embryo must first break out of the zona. This is known as hatching.
If you look at the embryo during different stages of its development,
you might notice that the thickness of the zona changes. During the first few days of development,
when the embryo is between 1 and 8 cells, the zona is thicker. At the blastocyst
stage which occurs after 5 or 6 days of development, the zona becomes very thin.
In the early days of IVF, there was concern that embryos grown in the lab might have a
harder zona that was more difficult to break out of. This was called zona hardening. Some
scientists thought that making a hole in the zona or thinning it out a little might help
the embryo to escape and that this might increase the chance for a pregnancy. This became known as
assisted hatching. You might see this acronym AZH which stands for assisted zona hatching.
Over the years, there have been a number of different techniques that have been described
all under the umbrella of assisted hatching. First, there are three
techniques used to perform assisted hatching. Some centers use acid to dissolve the zona.
Some may use a glass pipette to create an opening. Other centers, such as here at IVF1,
we use a laser. There are a lot of differences in how much of the zona is treated. For example,
some centers may just thin the zona rather than create an opening. The
thinning could be just at one spot, or be extended to a larger size such as
one fourth of the circumference of the embryo or even one half -- such as you see here.
Some IVF programs will pierce the zona to create an actual opening. Just like we saw with thinning,
this opening could be at one spot,
or a larger area encompassing one fourth or one half of the zona.
Does the use of assisted hatching increase the chance that an embryo will implant? It turns
out this is a very difficult question to answer. Consider this, some IVF programs transfer fresh
embryos while others transfer frozen embryos. Even if an assisted hatching technique helps for one,
there is no guarantee it will work for the other.
Remember earlier I said that the thickness of the zona changes during embryo development?
Well that means it is possible that assisted hatching could be helpful
if transferring embryos at one stage but not at another.
Complicated enough? Just wait! There’s more! Some IVF programs may fertilize
eggs by adding sperm to the outside of the egg. Other times, we may use a technique called ICSI,
where we inject sperm directly into the egg. When we inject a sperm, we are creating a small
hole in the zona which is essentially the same process used to make a single opening during
assisted hatching. Does that mean assisted hatching is not needed when ICSI was used?
We also create a hole in the zona when we are biopsying an embryo
to do preimplantation genetic testing. How does that impact the process?
There have been a number of studies done trying to determine whether assisted hatching
improves pregnancy rates. Some studies have found a benefit, others have not.
Attempts to combine smaller studies into a larger study, which is known as a meta analysis,
have not been conclusive because there are so many different techniques and variables.
So what is the bottom line? There is an abundance of low quality evidence that assisted hatching
improves the chance for having a baby. There is little to no high quality evidence however.
Some of you might be thinking, well it might help.. Is there any harm? Well…Possibly! If
not done correctly, exposing an embryo to an acid solution may harm the embryo.
Using a laser might raise the temperature of the embryo too much and also cause some harm.
Our Infertility TV Bottom Line is this. Assisted Hatching is a common technique
used by IVF programs all over the world. At this point, however, there is no clear,
high quality evidence that it is helpful and if it is helpful, under what circumstances and with
what techniques. It is possible that we may never know for sure. Until then,
IVF patients and their doctors will have to make these decisions with the evidence that we have.