The word IMSI is the acronym for Intracytoplasmic Morphologically Selected Sperm Injection. It is a technique used in assisted reproduction derived from the well-known ICSI (Intracytoplasmic Sperm Injection") whose fundamental difference lies in the fact that in this case the spermatozoa chosen are selected depending on their appropriate morphology. In short, we could say that it is an improved ICSI, since this morphological selection is carried out thanks to a lens in the electron microscope that allows the spermatozoa to be viewed at much higher magnification.
Specifically, IMSI offers a magnification of more than 6,000 times, compared to traditional ICSI, whose maximum magnification is 400x. In this way it is possible to observe in detail the morphology of the gametes selected for microinjection.
This method of fertilization, i.e. ICSI, is the most common, especially in cases of severe male factor. However, this technique presents certain subjectivity, since each specialist chooses the spermatozoa according to his own criteria by observing their head, tail and intermediate segment.
Thanks to the appearance of IMSI and the improvements it brings to the sperm analysis and selection procedure, the pregnancy rate has increased in cases of male infertility. Thus, spermatozoa are discarded which, although they have the capacity to fertilize, due to their poor morphology could cause implantation failure (greater risk of spontaneous abortion). Therefore, motile spermatozoa, without alterations and without vacuoles in the nucleus, are selected.
Specifically, IMSI is recommended in the following cases:
- males with severe oligoasthenoteratozoospermia.
- High sperm DNA fragmentation.
- long-term infertility of unknown origin.
The procedure for IMSI is the same as for ICSI. Semen is capacitated in the laboratory and resuspended in the appropriate concentration. The only change is the microscope that is used to select the sperm morphologically with IMSI. This microscope is based on MSOME (Motile Sperm Organelle Morphology Examination) technology and is equipped with a digital image processor. Once the spermatozoa of interest to the embryologist have been selected, they are transferred to the ICSI plate and taken to the conventional microinjector to fertilize the eggs in the same way.
Therefore, we can conclude that, a priori, no special preparation is required in cases that are going to undergo IMSI.