Intracytoplasmic Sperm Injection of the Eggs
Intracytoplasmic sperm injection, or ICSI, refers to the placement of a single sperm directly into the cell material, or cytoplasm, of the egg by the embryologist. This process becomes necessary when the penetration of the shell and inner membrane of the egg by the sperm is not likely to happen.
If the sperm quality dictates that fertilization of the eggs can only occur with ICSI, the maturity of each egg must be known before the injection is performed. Four to six hours after the retrieval, maturity of the eggs is assessed by removing the cumulus cells. Maturity of an egg is defined as an egg that has reduced its number of chromosomes by half. The purpose of this reduction process is to allow the other half of the chromosomes to come from the sperm when it enters the egg. The way that maturity is determined by the embryologist is by looking for the presence of a little round body located on the edge of the egg. This round body is known as a polar body. It contains the half of the egg’s chromosomes that it has expelled during its process of maturation.
The examination of the eggs before ICSI allows the embryologist to know more about the eggs than would have been known if the eggs were fertilized by insemination. Because of this examination, some eggs are eliminated from the process before sperm is injected into them. These eggs are the immature, degenerate (called atretic), and broken ones. The ICSI process does not eliminate more eggs than if the eggs had been inseminated. It just eliminates them BEFORE they would have been identified as non-viable with the insemination process. So, it is not unusual to have retrieved 12 eggs for a patient and to have only 10 injected.
Once the mature, healthy eggs have been identified, the ICSI procedure can begin. A small population of the best sperm available from the prepared sample is placed in a thick, syrupy solution called PVP. This allows for a thorough visual examination of the morphology, or shape, of the sperm while they swim in a slow, undulating motion. Meanwhile, the eggs have been placed in drops of medium in the same dish. The medium that the eggs are placed in for the ICSI process is specifically designed to keep the pH stable while the eggs are out of the incubator.
When the embryologist has placed the two glass micro tools on to the micro manipulators, one for holding the egg and one for injecting the sperm into the egg, the process can begin.
First, a sperm is selected based on its movement and normal shape. The injecting pipette is dragged carefully across the tail of the sperm, breaking its outer membrane. The sperm is then picked up in this injecting pipette and taken to the drop containing the egg. The egg is held with a holding pipette that provides a gentle suction to its shell. Then, the injecting pipette is pushed gently into the egg, breaking its membrane. The sperm is injected into the interior of the egg and the pipette is removed. The suction of the holding pipette is released and the eggs are returned to the incubator after all of the eggs have been injected.