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.
Washed sperm are viewed at a magnification 6000-12,000 times than their normal size. This greater magnification shows irregular features in sperm heads that otherwise cannot be seen. The embryologist then chooses sperm with the most normal looking heads.