IMSI is based on a method of high magnification motile sperm organelle morphology examination (MSOME). It requires an inverted light microscope equipped with high power Nomarski optics enhanced with digital imaging. Such examination helps to identify spermatozoa with a normal nucleus and nuclear content. The exact indications of IMSI and usefulness are debatable. Finding normal-looking spermatozoa took a minimum of 60 min, and up to 210 min, depending on the quality of the semen sample. The IMSI procedure improved embryo development and the laboratory and clinical outcomes of sperm microinjection in the same infertile couples with male infertility and poor embryo development over the previous ICSI attempts.

Introduced in 2001, intracytoplasmic morphologically selected sperm injection (IMSI) represents a more sophisticated way of ICSI whereby, prior to injection, the spermatozoon is selected at higher magnification. Doing so, the spermatozoon can be evaluated for fine integrity of its nucleus and the injection of a normal spermatozoon with a vacuole-free head can be assured. 

Additional research is needed to unravel the underlying mechanisms responsible for the presence of vacuoles in sperm heads. Vacuoles in human sperm cells appear in various numbers and sizes, both in abnormal-shaped spermatozoa as well as in normal-shaped spermatozoa. Associations with acrosome status, chromatin condensation, DNA fragmentation and sperm aneuploidy have been documented, however, controversy on their nature exists. Spermatozoon shape and large vacuoles are detected and deselected in conventional ICSI as well. However, the detection of subtle small vacuoles depends on the resolving power of the optical system and may impact oocyte fertilization, embryo development and implantation. 

Several comparative studies have indicated that the use of high-magnification sperm selection was associated with both higher pregnancy and delivery rates, whereas also lower miscarriage rates were observed. However, still to date randomized, well-powered studies to confirm these findings are scarce and show conflicting results. Hence, the most relevant indications for IMSI still remain to be determined. Two groups of patients have been put forward i.e. severe male-factor infertility patients and patients with a history of repeated ICSI failures. However, for both groups limited to no proof of any benefit does exist. 

The IMSI may improve the chances of fertilization in vitro and can use it if you have performed several IVF without success.

IMSI is a time-consuming procedure at the expense of oocyte ageing. The lack of proof and understanding of its benefit does not justify its routine clinical application at present.

As the technique seems not effective for any unselected ART patient, relevant indications for the use of IMSI need to be defined. For severe male factor patients, evidence suggests a higher clinical pregnancy rate with IMSI. The benefit for repeated ICSI failure patients, however, remains unproven.

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IMSI ―by Clinica Eugin Barcelona licensed under CC BY-SA 3.0
IMSI inmovilización del espermatozoide.jpg ―by Clinica Eugin Barcelona licensed under CC BY-SA 3.0
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