Finding sperm in the testicular tissue can be a laborious process, depending on the degree of sperm production, and for some men with partial testicular failure, it can take upto 2-3 hours to find the sperm. Also, testicular sperm are technically hard to work with in the laboratory and only some IVF clinics have the requisite expertise. For men with nonobstructive azoopsermia, some clinics perform the TESE the day prior to egg retrieval, because they believe culturing the testicular tissue in the incubator for 24 hours helps the sperm to acquire motility, which makes them easier to work with. In case no sperm are found, either the couple decides to cancel the egg retrieval and abandon the cycle, or to go ahead with using donor sperm for IVF, as a backup option.

In patients in whom surgery needs to be performed in order to recover testicular or epididymal sperm, it is now possible to freeze the excess sperm. These sperm can then be thawed and used in future cycles in needed, thus sparing the patient the need for repeated surgery for sperm retrieval.

Once eggs and sperm have been collected, the actual process of injecting a single sperm into the egg is carried out in a laboratory. The injection is performed on a heating stage, on a specialized inverted microscope (which allows one to magnify details up to 400 times) equipped with Hoffman modulation contrast optics (which enhance "optical contrast", so that the details of the egg can be visualized easily). The precise control that is needed for microinjection is provided by using specialized micromanipulators, which allow one to execute very fine movements.

The eggs and sperm are manipulated using fine glass pipettes, made of thin capillary tubing, which are even finer than a human hair. These are custom made, the holding pipette being designed to hold a single sperm. Live sperm are placed in a drop of viscous polyvinyl pyrrolidone (PVP) solution, which serves to slow down the activity of the sperm. (It is helpful to slow down the sperm, so that they can be picked up more easily by the injecting needle.) A single sperm is then selected and its tail is pinched or broken to immobilize it. This is usually done by crushing the sperm tail by rolling it between the injection pipette and the base of the petri dish. It is essential to immobilize the sperm, so that it cannot move after it has been injected into the egg. A single immobile sperm is then picked up by sucking it into the injection pipette.

The egg is secured in place by applying gentle suction to its shell (the zona) with a holding pipette. The sperm is then injected directly into the centre (cytoplasm) of the egg by moving the injection pipette very precisely with the help by moving the injection pipette very precisely with the help of the micromanipulator into the egg, and then blowing the sperm out very gently into the cytoplasm of the egg. In order to do this, it is important to breach the zona of the egg and the outer membrane of the egg. The skill of the embryologist is a critical factor in the success of the ICSI process. After injecting the sperm, the pipette is withdrawn. Remarkably, once the injecting pipette is withdrawn, the egg will close and assume its original shape within 60 seconds. One can visualize ICSI as the sperm being given a "piggyback" ride into the egg, so that what the sperm cannot accomplish on its own, the laboratory does for it! The only requirement for ICSI is that the sperm should be alive, and there should be as many sperm as there are eggs.

Once all the eggs are injected with a single sperm each, they are placed in the CO2 incubator, and then observed approximately 14 hours later to see if fertilization has taken place. If fertilization has occurred, the 2-4 cell embryos can be transferred into the wife’s uterus about 48-72 hours after ICSI, as is done for IVF. Interestingly, embryo implantation rates in these patients are quite high, because the wives are usually young and completely normal.

Fertilization rates in the range of 60-80 per cent have been achieved in experienced hands-which means, of 100 microinjection eggs about 60 form embryos after ICSI. In fact the technology is now reliable enough to virtually guarantee fertilization, if there are sufficient good quality eggs. The pregnancy rate in one ICSI cycle is about 35 percent. Remarkably, the chance of achieving a pregnancy does not depend upon the sperm count or number (since you only need as many sperm as there are eggs!), but rather on the number and quality of eggs retrieved, which, in turn, depend upon the woman’s age. The risk of having a baby with a birth defect is not increased with this technique.

What are the risks of doing ICSI?

More than 100,000 babies have been born worldwide after ICSI, and detailed studies have shown that there is no increased risk of birth defects or genetic anomalies, as a result of the technique.
It is possible, however, that some of the male children born as a result of this technique may be infertile as well (for example, if the cause for the testicular failure is a defective genetic locus, such as a microdeletion on the Y chromosome).