ICSI is commonly known as “second-generation IVF”, while conventional in vitro fertilization (IVF) is known as “first-generation IVF”, and second-generation IVF is not an upgrade of or a replacement for first-generation IVF. Intracytoplasmic Sperm Injection (ICSI) is a technique that helps many men with infertility by injecting sperm directly into the cytoplasm of the oocyte to achieve pregnancy. Infertility caused by male factors (such as severe oligospermia, weak and malformed spermatozoa, obstructive azoospermia, etc.) can be well resolved by ICSI. So let’s learn more about some of the problems of ICSI. 1.What is intracytoplasmic single sperm injection (ICSI)? According to statistics, infertility couples currently account for about 10% of couples of childbearing age, and about 40% of them are caused by male factors. These male infertility factors include: low sperm, weak sperm and sperm malformation. These factors lead to the difficult problem that sperm do not cross the zona pellucida of the oocyte to achieve sperm-egg union during in vitro fertilization, and that fertilization is not possible or is low. In 1992, Palermo, a Belgian researcher, created the historic ICSI technique, which was a breakthrough in human assisted reproduction technology and therefore won the Nobel Prize in Medicine. Since then, ICSI technology has been introduced into IVF treatment, that is, the use of special instruments and microinjection needles, artificial sperm through the oocyte zona pellucida, directly injected into the oocyte, to achieve fertilization purposes. 2.What people need to do ICSI? According to the relevant documents of the Ministry of Health of China, the indications for ICSI include: severe oligospermia, weakness and malformation of sperm; irreversible obstructive azoospermia; spermatogenic dysfunction (excluding those caused by genetic defects); immune infertility; failure of conventional in vitro fertilization; abnormal sperm acrosome; patients who need to undergo preimplantation embryo genetic examination and treatment. 3.What are the sperm requirements for ICSI? The sperm is divided into head, body and tail, as haploid cells, very tiny, about 50 microns long, the head is oval, about 3.5-5.0 microns long, about 2.5-3.2 microns wide, the length to width ratio is roughly 1.3-1.8, the acrosome area accounts for 40%-70% of the head area, the tail may be curved, but not bent at an angle. 4.How does ICSI select sperm? (1) “Face” pass the selection of sperm should be as far as possible to select normal morphology of sperm (to pick handsome), and can not be HE staining of sperm (common staining methods for cell and histopathology). (2) Healthy and active sperm is not enough, but the embryologists select sperm based on their activity status. Preferably, forward-moving sperm, and in special cases such as complete immobility (sperm cilia immobilization syndrome), a hypotonic swelling test can be performed to select viable sperm. Currently, in most fertility centers, sperm selection is done under an inverted microscope at 200x or 400x to select sperm with normal morphology and motility during routine ICSI operations. Although the embryologist selects a “normal looking” sperm, it does not guarantee that the egg will be fertilized after the injection. Many factors are involved in fertilization, such as whether the sperm and egg have normal chromosomes, whether the egg is mature or not, and whether the egg is activated. Therefore, ICSI does not guarantee 100% success in the union of each selected sperm and egg.