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 procedure is done under a microscope using multiple micromanipulation devices (micromanipulators, microinjectors and micropipettes). A holding pipette (on the left of picture) stablizes the mature oocyte. From the opposite site a thin, hollow needle is pierced through the oolemma and into the inner part of the oocyte. It is loaded with a single sperm that will be released 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 any specific testing. However, in mid 2006 the FDA cleared a device that allows embryologists to select mature sperm for ICSI based on sperm binding to hyaluronan, the main constituent of the gel layer (cumulus oophorus) surrounding the oocyte. The device provides microscopic droplets of hyaluronan hydrogel attached to the culture dish. The embryologist places the prepared sperm on the microdot, selects and captures sperm that bind to the dot. Basic research on the maturation of sperm shows that hyaluronan-binding sperm are more mature and show fewer DNA strand breaks and significantly lower levels of aneuploidy than the sperm population from which they were selected.

There is some suggestion that birth defects are increased with the use of IVF in general, and ICSI specifically. It is hoped that use of new device (PICSI) will lower the apparently elevated level of birth defects associated with ICSI.(see section of IVF discussing birth defects)

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