IMSI is a real-time method where sperms are selected before the microinjection takes place. This is done using an inverted microscope that is able to provide a much greater magnifying power (around 6,000 times) than those that are normally used in reproductive laboratories (400 times) to carry out the ICSI.
With this microscope, Biologists can see the internal morphology of sperm and discard those with abnormalities. Being able to select sperm without morphological alterations are believed to increase the chances of successful implantation of pre-embryo and decrease the likelihood of miscarriage.
The IMSI may improve the chances of fertilisation in vitro and can use it if you have performed several In Vitro Fertilization, IVF, without success.