ICSI is a micromanipulation technique introduced in clinical practice to solve cases of infertility due mainly to severe male factor infertility, but it is also indicated in the case of previous failures with IVF-ET and in the case of limitations on the number of oocytes available for insemination. There are no substantial differences in the preparation of a cycle of ICSI compared to traditional IVF, except for what concerns the laboratory procedures.
This technique consists in mechanically removing all oocyte barriers constituted by the cells of the cumulus and corona radiata, and introducing a single spermatozoon selected directly inside the oocyte cytoplasm. This procedure requires a laboratory instrument called micromanipulator. At our center there are two latest generation ultra-high definition micromanipulators equipped with laser and polarizer.
ICSI offers the great advantage of being able to observe and select the gametes (oocytes and sperm) before use.
Oocyte assessment: Polscope
The oocyte is assessed according to two criteria: nuclear maturity and morphological appearance.
The oocyte is considered to be mature (from the nuclear point of view), and hence usable for in-vitro insemination, if it has reached the metaphase II stage. At this stage the oocyte features the meiotic spindle (a birefringent structure consisting of microtubules that keep the oocyte chromosomes along on the metaphase plate). A study conducted at our center (Rienzi et al., 2003) showed a correlation between the presence and position of the meiotic spindle analysed using a special instrument (Spindle View) and the potential for development of the oocyte subjected to ICSI.
From a morphological point of view, the oocyte cytoplasm may have different types of polymorphisms: graininess, presence of organelles or vesicles, accumulation of smooth cytoplasmic reticulum, presence of areas of the cytoplasm with no organelles and/or vacuoles. Our team has recently demonstrated a correlation between some of these characteristics and the growth capacity of oocytes (Rienzi et al., 2008). At our center we select oocytes not only based on their maturity, but also on their quality.
In some cases in the presence of oocytes with particular morphological characteristics Laser-ICSI can be performed (Rienzi et al.). This technique allows thinning a small part of the outer membrane of the oocyte (pellucid zone) using a laser to reduce the pressure exerted during the injection. This reduces the mechanical stress due to the injection which can damage the more fragile oocytes, compromising their survival.
Sperm assessment: IMSI
Spermatozoa are usually observed and selected at a magnification of 400 times. In some cases, to carry out a more accurate selection, it may be necessary to perform IMSI, which stands for intracytoplasmic morphologically selected sperm injection. It consists in the evaluation of the quality of individual spermatozoa at very high magnification. This makes it possible to identify morphological abnormalities such as vacuoles and nuclear defects.
In assisted fertilization routine the selection of embryos with the best potential for growth and development relies mainly on static observation of morphological criteria such as the number and size of the blastomers and percentage of fragmentation. However, this method does not allow identifying the subtle differences between one embryo and another as for example the time that the embryo employs between one division and the next.
The use of automated instruments that allow the continuous capture of images and the video reconstruction of the entire embryonic development cycle while providing an optimal culture environment has allowed us to reconcile the need to obtain more detailed information regarding the development of each individual embryo with the need not to expose it to less than optimal environmental conditions that could jeopardise its viability.
The possibility to carry out a dynamic assessment of the whole embryo development process, from fertilisation to the blastocyst stage, is helping us to identify new evaluation criteria that may be more predictive of an embryo’s development and implantation potential.