Intracytoplasmic sperm injection (
ICSI, pronounced , ) is an
in vitro fertilization procedure in which a single
sperm is injected directly into an
egg. Defective sperm function remains the single most important cause of human infertility (). Although certain severe forms of male infertility have a genetic origin, others may be the result of environmental factors. During the past decade, ICSI has been applied increasingly around the world to alleviate problems of severe male infertility in human patients who either could not be assisted by conventional IVF procedures or could not be accepted for IVF because too few motile and morphologically normal sperm were present in the ejaculate of the male partner ().