- In IMSI, an x63 objective (63x magnification) or an x100 objective (100x magnification, but this is a rare case) is used. In ICSI – an x40 objective;
- In IMSI, another type of contrast is employed – DIC. In ICSI it is PhC or MC;
- In IMSI, the image is displayed on a computer screen. Yet nothing stops you from doing that with other methods as well.
On the one hand, there are a number of papers showing that a careful selection of sperm cells with all morphological details taken into account, including the presence and the form of vacuoles, improves the results of ICSI.
On the other hand, there is not a single meta-analysis (an independent analysis of all available papers on the issue) that would show statistically significant advantages of IMSI over standard ICSI.
So what is it all about?
- There is no one way to perform simple ICSI. If you take just any sperm cell, the results will be, of course, disappointing. However, a careful selection of “good” sperm cells in simple ICSI, as a rule, solves most problems;
- When talking about IMSI, the main emphasis is put on the possibility of selecting sperm cells without vacuoles, i.e. with a lower DNA fragmentation.
In fact, the appearance and disappearance of small vacuoles in a sperm cell is a normal physiological process. The main thing about it is that they should not be very prominent. If required, the largest vacuoles can be seen in simple ICSI as well. The smaller ones that are visible only in IMSI are not so bad, and are often not bad at all.
Besides, the advantages of IMSI partially overlap with other methods.
Why do we actually need IMSI? - To select sperm cells that would provide maximum quality embryos when used for fertilization.
What do we need for it?
- Sperm cells should undergo all maturation processes (disposal of excessive cytoplasm, DNA repackaging, the replacement of histones by protamines, centriole formation etc). Whether these processes have taken place can be judged by cell morphology (IMSI) or partially by morphology (simple ICSI) and partially by the appearance of specific receptors on the surface of a sperm cell (PICSI).
- There should be no destructive processes in sperm cells under way. Whether there are any can also be judged by morphology – the appearance of large vacuoles (IMSI) or by the appearance of specific substances in the external layer of a membrane (sperm cell selection based on binding to annexin).
- During spermatogenesis, there should be no outright “breaks” (aneuploidy, DNA fragmentation etc). At the moment, this can only be judged by morphology.
And not only because we do not know everything, but because many tests cannot be run on live sperm cells. For instance, we can learn about genetic anomalies only by having “utilized” the entire genome of a sperm cell; DNA fragmentation can only be assessed with the help of fixed (i.e. dead) cell preparations et cetera. This sounds just like Bohr. The complete knowledge of a system is impossible without its destruction.
This is when IMSI can offer some advantage. Still, it cannot fully guarantee the “absence of breaks”.