In ICSI, a single sperm is injected into a harvested egg to artificially fertilize the egg.

Intracytoplasmic sperm injection, or ICSI, is a specialized laboratory technique that allows for the injection of a single sperm (spermatozoa) into an egg in order to achieve fertilization. In standard in vitro fertilization (IVF), between 50,000 and 100,000 sperm are placed in the same dish as a single egg, and sperm are allowed to naturally fertilize the egg. In the event that no abnormalities in the sperm exist, normal fertilization is often confirmed the next morning. However, in cases of male factor infertility where significant abnormalities in the count, motility, and/or shape of the sperm exist, IVF results in very poor fertilization rates, often resulting in no fertilized eggs and thus no embryos for transfer. Since ICSI involves the injection of only a single sperm into each egg, even the most severe of male factor abnormalities can be overcome. Using special micromanipulation tools, a single morphologically normal motile sperm is immobilized, loaded into a fine hollow needle, and carefully injected through the eggshell (zona pellucida), membrane, and into the center (cytoplasm). Fertilization rates with ICSI are generally excellent, on the order of 75-85%.

Various indications have evolved over the years for ICSI. In addition to male factor infertility, ICSI has successfully been employed in cases of unexplained infertility, prior fertilization failure, anti-sperm antibodies, and in cases where only a small number of eggs are available for fertilization. Numerous clinical trials and studies have illustrated the safety of ICSI.