ICSI or Intracytoplasmic Sperm Injection is a type of In Vitro Fertilization that is used to fertilize the egg cell. With ICSI, the sperm cell is selected and injected within each one of the eggs collected.
Unanimously recognized indications of ICSI include:
Severe male infertility: a single sperm per egg cell is enough
Previous fertilization failure using conventional IVF
Issues with the oocytes: poor-quality eggs may compromise sperm penetration into the egg cell
Techniques that involve isolating the egg from the cells that surround it (egg donation, preimplantation diagnosis...)