IMSI (Intracytoplasmic Morphologically Selected sperm Injection)
Intracytoplasmic morphologically selected sperm injection (IMSI) is a variation of ICSI that uses a higher-powered microscope to select sperm. This allows embryologists to look at the sperm in greater detail including the nucleus which contains the sperm’s genetic material. This is done using an inverted microscope that is able to provide a much greater magnifying power (around 6000 times) than those that are conventionally used in reproductive laboratories (400 times) to carry out the ICSI.
ICSI method of treating predominantly male-factor patients achieved a breakthrough and it established itself as the preferred method of treatment in the field of assisted reproduction. When ICSI is used in the routine way, one sperm is taken after routine selection under a regular microscope that magnifies 200 to 400 times.
Sperm morphology has been recognized to be a crucial factor for the efficiency rate of fertilization, pregnancy and birth rate. Examination of spermatozoa with the light microscopy can provide only limited information on their internal structure. Using conventional magnification, only sperm morphology can be visualized, but not the sperm nuclear abnormality. Several studies have demonstrated a positive correlation between optimal sperm morphology and positive ICSI outcomes. In fact, spermatozoa with severe abnormalities of the head are well documented to be associated with low fertilization, implantation and pregnancy rates. However, a spermatozoon which is classified as ‘normal’ by microscopic observation at (x200-400) low magnification could contain ultra-structural defects that impair both the fertilization process and embryonic development. These anomalies can be defined in an andrology laboratory with special staining techniques, but spermatozoa cannot remain viable after staining and cannot be used for microinjection.
The intracytoplasmic morphologically selected sperm injection (IMSI) procedure changed the perception of how a spermatozoon suitable for injection should appear. Sperm selection is carried out at (×6000-7000) high magnification, allowing improved assessment of abnormalities of the head and the sperm nucleus. During IMSI, a very high power microscope equipped with high resolution optics enhanced by video zoom and digital imaging system is used to magnify the sperm over 6000 times. This allows us to see in great detail how the sperm looks and to select the best sperm. Once the best sperm has been selected the IMSI procedure is carried out in exactly the same way as ICSI. IMSI is a very new development and is showing promise for a specific group of patients.
The morphological disorders in the DNA structure of the head of the sperm will cause some fertilization problems such as IVF failure, embryo development arrest or slow development of embryo. Studies on the sperm head including the genetic material within the nucleus have been carried out intensively since 2005 in order to detect the abnormalities in the sperm head. Intracytoplasmic morphologically selected sperm injection (IMSI) allows the motile-sperm organelle-morphology examination (MSOME), by which the fine nuclear morphology of motile spermatozoa is examined in real time with an inverted light microscope equipped with high-power differential interference contrast optics enhanced by digital imaging to achieve a total magnification of over 6000 times. The criteria for normally shaped nuclei are smooth, symmetric and oval configuration, with average length and width limits with no regional nuclear disorders, and containing no more than one vacuole. Two highly morphologically selected sperm cells are collected for each ova expected to be retrieved.
As a conclusion, microinjection of sperm with abnormal shape or nuclear vacuoles appears to reduce pregnancy outcome. This drawback can be prevented by morphological sperm selection.