Intracytoplasmic sperm injection (ICSI) is an in vitro fertilization procedure in which a single sperm is injected directly into an egg; this procedure is most commonly used to overcome male infertility problems.
The cumulus cells that surround the egg are removed using an enzyme called hyaluronidase, this historically comes from bovine testis but new technology has provided a pure recombinant product that is now available.
A small amount of washed sperm is placed into thick viscous media containing poly vinyl pyrrolidone (PVP) in a dish. The PVP slows the sperm down so that they can be morphologically assessed. The most normal looking sperm are selected and then immobilized by squashing their tales with a glass injection needle. The sperm are sucked into the needle tail first ready to be injected.
The egg is then placed under a microscope and moved using micromanipulation devices (micromanipulators, microinjectors and micropipettes). A holding pipette stablizes the mature oocyte then from the opposite site a thin, hollow glass needle is pierced into the inner part of the oocyte. it is loaded with a single sperm that will be expelled into the oocyte. The pictured oocyte has an extruded polar body at about 12 o’clock indicating its maturity. After the procedure, the oocyte will be placed into cell culture and checked on the following day for signs of fertilization.
In natural fertilization sperm compete and when the first sperm enters the egg cell, the egg cell blocks the entry of any other sperm. Concern has been raised that in ICSI this sperm selection process is bypassed and the sperm is selected by the embryologist without undergoing any specific testing.
Reasons for ICSI:
- Sperm completely absent from the ejaculate (azoospermia)
- Sperm present in low concentrations (oligospermia).
- Poor sperm motility (asthenospermia)
- Poor sperm morphology (teratospermia)
- Sperm retrieved by surgical techniques (for example TESA, TESE)
- Problems with sperm binding to and penetrating the egg
- Antisperm antibodies
- Previous failed or poor fertilization
- Unexplained infertility
- Frozen sperm limited in quantity
- If preimplantation genetic diagnosis (PGD) is being used to screen embryos for a specific genetic disorder