The acrosome reaction test has much prediction of IVF fertilization than the semen analysis. We do not have perfect tests but I will show you that the acrosome reaction test helps us reduce the need for ICSI. The AR test gives us a very good idea of which men have sperm that will fertilize the eggs without assistance.
When the sperm reaches the egg, it must lose it’s acrosomal cap in order to bind to the shell around the egg (zona pellucida) and pass through the zona and then fertilize the egg inside.
The AR Test is used to predict whose sperm will likely fertilize the egg, and whose sperm will not. Dr Richard Sherins and his team developed this test in the 1980’s and they validated the results of the test by comparing them to the IVF fertilization rate.
On the left, is a photograph with the acrosome cap highlighted. On the right, is a photograph of the sperm using a fluorescence microscope. The sperm with a dark tip have undergone the acrosome reaction artificially while those that are bright green did not react. We calculate the percentage of sperm that artificially react in the assay.
Many labs can induce the acrosome reaction test but the question then is what do these results mean? The assay that we use was validated with human IVF in the days before we had ICSI. Back then we did not have a reliable method to get the sperm into the egg, so we were able to compare the results of the lab test to the actual outcome measure of interest – fertilization of eggs. While not perfect, the assay has allowed us to almost eliminate failed fertilization at IVF and limit the use of ICSI if the sperm are capable of unassisted fertilization.
In the early 1990’s, embryologists became skillful at inserting a single sperm into an egg to allow fertilization to occur when the sperm could not get into the egg on its own power. The technic is called IntraCytoplasmic Sperm Injection (ICSI). ICSI enables “poor quality” sperm to fertilize eggs at the same rate as normal sperm. Just as importantly, the children are normal. Since the development of ICSI, we have lost the ability to validate SA tests because it would be unethical to withhold ICSI if the sperm seems abnormal.
The unexpected low fertilization that occurs with what appears to be a normal semen analysis is why many IVF clinics use so much ICSI. They and their patients hate to have low fertilization, low numbers of embryos and possibly lower pregnancy rates. This is why ICSI rates are 0ver 60% in the US right now!
In this graphic we show you that conventional IVF fertilization is normal when the AR score is normal. In this case, the results of the sperm analysis is irrelevant. The circles show you the median fertilization and the boxes show the range of fertilization rates from the 25th percentile to the 75th percentile.
In this graphic I show you that the fertilization rates remain normal even when the sperm morphology is very poor but the AR test score is normal. The circles show you the median fertilization and the boxes show the range of fertilization rates from the 25th percentile to the 75th percentile.
Please note two important findings:
- If the man has 3 abnormal parts of the semen analysis, then he has a very high chance of an abnormal AR test. He also has a chance that he does not need ICSI if he is in the 15% of these patients with a normal AR test.
- Even a man with a completely normal semen analysis has a chance of a failed or abnormal AR test. Recall that I earlier showed you that 33% of our abnormal AR tests have “normal strict sperm morphology scores”.
The AR Test helps us identify men whose sperm will likely NOT fertile eggs well and they need treatment to improve sperm quality or IVF/ICSI. The AR Test also identifies men who have normal sperm function and who do not need ICSI even if IVF is needed for other reasons. These men can confidently attempt non-IVF treatment.
We feel that the AR test allows us to make rational evidence based decisions. We feel that the test allows us to avid ICSI at least 20% more often than most IVF centers. You should check for this fact as you choose your IVF center. The data is easy to find on the IVF clinic’s profile at SART website.