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 If you liked this video, please **LIKE** this video and you should definitely subscribe to InfertilityTV now for new episodes
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