Intracytoplasmic sperm injection (ICSI) is a procedure used to fertilize eggs with sperm. It is often used when there is concern that natural fertilization may not occur if eggs are exposed to sperm as a result of In Vitro Fertilization (IVF). ICSI is performed by an embryologist with the aid of a microscope and special tools. In the procedure, a sperm is injected into an egg with a very fine needle controlled by the embryologist looking through the microscope.