IMSI (Intra-Cytoplasmic Morphologically Selected Sperm Injection) is a technique that was introduced in 2001 and is used throughout the world. It is an extension of ICSI (Intra-cytoplasmic sperm injection), which is performed by selecting the most normally-shaped (morphologically normal) sperm found at a magnification of approximately 400x. In comparison, IMSI uses a much higher magnification (approximately 6000x) and allows the scientist to assess and select the spermatozoa to be used for injection using a strict-criteria where possible consisting of the following:
- a normal nucleus (where the sperm’s DNA is located), that has a defined oval shape and smooth configuration
- less than 4% of the nucleus occupied by vacuoles. Vacuoles are found in almost all sperm heads even with normal morphology, they are poorly understood in their role in male fertility, however the location, number and size of these vacuoles may have a direct correlation with high levels of DNA fragmentation and damage and therefore are to be avoided where possible.
How Is IMSI Performed?
The technique is performed using a conventional ICSI microscope, but with high-powered optics, which is then further enhanced to a magnification of 6600x. In addition, a glass bottom dish is used to be able to gain clear vision of the spermatozoa during the selection and injection process.
Photo 1: Normal sperm – normal morphology with no or minimal small vacuoles (<4%)
Photos 2-5: Abnormal sperm – with varying degrees of poor morphology and/ or vacuoles (=/> 7%)
Who May Benefit From IMSI?
IMSI is not recommended for all patients, as it has not been shown to improve outcomes in all patient sub-groups. In addition to this, there is additional handling of the spermatozoa involved when using this complex procedure which is time consuming, and subsequently may expose the oocytes (eggs) to unnecessary environmental changes (i.e. in temperature and pH) which should be avoided where possible.
IMSI has been shown to improve clinical pregnancy rates and decrease miscarriage rates in the following sub-groups of patients (Fertility Solutions only recommends use in these patients):
- Previous recurrent miscarriage/early pregnancy loss (a minimum of 2)
- Male factor infertility (including mid – high DNA fragmentation)
- Previous failed or multiple poor fertilisation outcomes after conventional ICS