There are two main reasons why the sperm concentration is too low. The first is that you remove too much supernatant when you centrifuge, and the second reason could be that you work – sorry – too slowly!  You will be surprised how fast the sperm regain motility after centrifugation. Instantly the sample stops, they swim out of pellet. Therefore, you must be ready to remove supernatant immediately after centrifugation.

To rescue the sample, so to speak, I would rather say that you can rescue your fertilization. As a general rule, you should not add more than10 ml sperm solution if you work with 100 ml drop – or 50 ml when you work in a 500 ml well. The reason is that you will dilute the IVF medium with sperm solution medium. However, what you can do to reach the recommended 2 mio/ml sperm concentration, is to add more sperm solution and then after one hour go back and remove 50 % of the medium – away from the oocytes, and then add fresh CO₂   equilibrated IVF medium.

There are several reasons why your oocytes have too few cumulus cells. It can be that the aspiration speed is too high, it can be that the aspiration tubes are too wide in diameter and that causes turbulence and will strip the oocytes of cumulus as they swirl through the tube. Also if the aspiration tube is too narrow, which is less often the case, this will also strip the cumulus off the oocyte.

And question 2 the answer is simple: YES! – it is extremely important for a successful maturation During maturation the cumulus expansion of the cumulus-oocyte complex, the COC is necessary for meiotic maturation and development and thus the subsequent fertilization process.