Sometimes, during IVF, the eggs don't fertilize. Why does this happen?
Stay tuned as we explore the reasons
We can divide fertilization failure into three categories
Number 1 - Problems with the sperm
Number 2 - Problems with the egg
Number 3 - A combination of these problems
Fertilization of an egg isn't just a single event
It is a series of events that must all occur in the correct order to end up with a viable embryo
When an egg is removed from the ovary during the egg retrieval process
it is surrounded by a large number of cells called cumulus cells
When sperm make first contact with the egg, they're not actually contacting the egg at all!
They are contacting the cells of the cumulus
Furthermore, hundreds of sperm may make contact with the cumulus at the same time
or within seconds of each other. The sperm must go through some important changes
which results in sperm activation - this helps the sperm bore through the cumulus cells
Underneath the cumulus cells, there is a hard shell of proteins that surround the egg called the zona pellucida
As the sperm approaches the zona pellucida some enzymes are released.
These enzymes dissolve the zona pellucida
to make a passage for the sperm to get through to reach the membrane of the actual egg cell
At some point, with some luck,
the surface of the sperm cell will meet and fuse with the surface of the egg cell.
The contents of the sperm are then released into the egg cell.
This is also a several step process
So, there are three major barriers that sperm must get past in order to release their contents into the egg
There are abnormalities that can occur in sperm that can cause one or more of these steps to fail
Fortunately, we have a technology called ICSI that can bypass these sperm problems
ICSI involves injecting a sperm directly inside the egg
As a result, ICSI is an excellent technique for bypassing any problems
which make it harder for a sperm to get inside the egg.
However, the process of fertilization is not yet over! Once the sperm releases its contents into the egg,
there are another several steps that have to occur.
This is the point at which problems with the egg can block completion of the fertilization process.
The egg must itself become "activated" , block additional sperm from entering,
start sorting all of the chromosomes from both the egg and the sperm...
and move the chromosomes to the correct spot.
It then has to allow the egg to divide
and the chromosomes have to start duplicating themselves
Even if a sperm is injected into an egg using ICSI,
problems within the egg may still prevent the process of fertilization from being completed
Unfortunately, we do not have accurate testing
which can identify which sperm or eggs may have abnormalities that will prevent fertilization
Using ICSI, we can bypass most, if not all, of the sperm problems, but not the egg problems.
There are no known technologies that can "fix" these sperm or egg problems
Unless technology changes dramatically, attempts at fertilization are never going to be perfect.
At IVF1, where we use ICSI for all of our IVF cases,
we see about 70 to 80% of the eggs we inject will fertilize
This is an average. We have seen some instances of 100% fertilization
and some instances, although rare, of 0% fertilization.
You probably have a lot more questions about IVF and fertilization and embryos
If you do, check out this video playlist
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