Intracytoplasmic Morphologically Selected Sperm Injection
The introduction of intracytoplasmic sperm injection (ICSI) procedures marked an important milestone in the development of assisted reproduction techniques. With this procedure patients whose semen samples were insufficient for intrauterine insemination or in vitro fertilization (IVF) could achieve pregnancy through the use of micromanipulation techniques under magnification.
Although oocyte quality has been a strong determinant for success in assisted reproduction, one potential problem with micromanipulation is the fact that the operator selects the spermatozoon for microinjection and therefore the natural selection barrier to fertilization is bypassed. Even more so, when the optic systems regularly used for IVF-ICSI (with a magnification of 200 a 400 X), although good for the evaluation of big cells such as eggs, are relatively limited to evaluate in detail small cells—such as spermatozoa; morphological features in the sperm head (such as vacuoles) and midpiece are not observable with these optics.
In order to overcome this situation computer-enhanced digital microscopy with a greater resolution (6000 X or more) has recently been introduced (1). This was originally applied to motile sperm cells and the analysis ‘Motile Sperm Organelle Morphology Examination’ (MSOME) developed to examine sperm cells potentially selectable for ICSI. With MSOME, subtle morphological features such as the presence of vacuoles in the sperm head and midpiece abnormalities have been characterized.
MSOME is stricter than the “strict” morphology assessment used for conventional ICSI and deselects spermatozoa that would otherwise have been used for ICSI. The application of MSOME for the selection of sperm for ICSI is termed “intracytoplasmic morphology selected sperm injection” or IMSI. Its use has been shown to increase pregnancy rates and reduce spontaneous pregnancy loss compared to previous failed ICSI cycles.
Since a correlation exists between the presence of large vacuoles in spermatozoa and DNA fragmentation, it is believed that IMSI “deselects” sperm with physiologic abnormalities related to DNA fragmentation.
Spermatozoa are considered morphologically suitable for ICSI procedures where the head of the sperm has a regular oval shape, 4.5–4.9 μm in length and 3.1–3.5 μm in width, and is characterized by a maximum of a single vacuole not more than 4% the total area of the sperm head. The midpiece is also required to be a regular, rectangular shape between 4.0 and 5.0 μm in length (Fig. 1).
The results of a recent meta-analysis demonstrated no significant difference in fertilization rate between ICSI and IMSI groups. However, a significantly improved implantation (odds ratio (OR) 2.72; 95% confidence interval (CI) 1.50-4.95) and pregnancy rate (OR 3.12; 95% CI 1.55-6.26) was observed in IMSI cycles. Moreover, the results showed a significantly decreased miscarriage rate (OR 0.42; 95% CI 0.23-0.78) in IMSI cycles as compared with ICSI cycles.. The pooled data of IMSI cycles demonstrate a statistically significant improvement in implantation and pregnancy rates and a statistically significant reduction in miscarriage rates (2,3).
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