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The intracytoplasmic morphologically selected sperm injection (IMSI) is a laboratory technique used for In Vitro Fertilisation treatments. High quality sperms are injected into the egg for fertilization, it is an advanced version of ICSI. A high powered microscope is used to pick out and the best sperm cells which are then used in a traditional ICSI protocol. In ICSI a magnification of x400 is used, while in IMSI an amplification of 6000 to 10,000 is used, at least 15 times greater. This allows the sperm to be examined in greater detail, including the nucleus which contains the sperm's genetic material. Use of this method has resulted in higher pregnancy and delivery rates and lower abortion rates. IMSI is a good choice for anyone who has failed IVF cycles in the past, and for couples who have a component of male infertility.
Introduced in 2001, the intracytoplasmic morphologically selected sperm injection (IMSI) procedure changed the perception of how a spermatozoon suitable for fertilization (via injection into the egg) should appear. A very high powered lens is used to see the sperm in greater detail during the selection process. The spermatozoon is selected at higher magnification; the aim of this is to improve the chance of pregnancy. The use of high magnification for morphological sperm selection prior to ICSI has been associated with higher pregnancy rates and lower miscarriage rate.
Spermatozoa can be considered morphologically suitable for ICSI procedures when the sperm head is regular oval, symmetric and with smooth appearance. It should be 4.5-4.9 μm in length and 3.1-3.5 μm. Nuclear chromatin mass should be homogeneous, with no more than one vacuole, or with a total vacuolar area of less than 4% of nuclear area. Also the central part has to be of a normal rectangular shape between 4.0 and 5.0 μm in length. The acrosome should ideally occupy between the 40-70% of the head.
Cases where IMSI may be used:
- High levels of DNA fragmentation.
- High levels of sperm aneuploidy.
- Men with severe oligozoospermia, asthenozoospermia or teratozoospermia.
- The egg quality has appeared to be normal.
- Repeated early abortions.
- In patients where there is a history of miscarriage.
- Previous ICSI fertilization failures.
- More than 90% of abnormal forms in sperm.
In a study, in which thirteen authors from nine different research centers and ART clinics form France, Israel and Spain participated and brought together a set of 9012 in vitro fertilization (IVF) attempts made in cases of male infertility, 3339 (37.1%) using conventional ICSI and 5673 (62.9%) performed using the IMSE technique. In 15.9% of the attempts made using ICSI no embryo was suitable to be transferred to the uterus of the patients; whereas in the case of the IMSE, this failure occurred only in 7.5% of the attempts. 
Despite the benefits that IMSI can bring, this technique has two very obvious drawbacks that are making it difficult to spread widely:
- The average extra duration of the procedure is considerable, ranging from 1.5 to 5 hours, since it is more difficult for the doctor to locate all the sperm with such a significant optical increase.
- Due to the high cost of the equipment, IMSI is not available in all IVF laboratories.
For all this, IMSI is only advisable when the specialist considers that the semen has a very poor quality, as well as in repeated cases of IVF or ICSI failures.
- Intracytoplasmic morphologically selected sperm injection (IMSI)
- Lo Monte, Giuseppe; Murisier, Fabien; Piva, Isabella; Germond, Marc; Marci, Roberto (September 2013). "Focus on intracytoplasmic morphologically selected sperm injection (IMSI): a mini-review". Asian Journal of Andrology. 15 (5): 608–615. doi:10.1038/aja.2013.54. ISSN 1008-682X. PMC 3881647. PMID 23832017.
- “Acquired Sperm DNA Modifications: Causes, Consequences, and Potential Solutions” (Tesarik, 2019)