What Is ICSI?

The letters stand for “Intracytoplasmic Sperm Injection.” This is the medical term for a procedure done by embryologists when they select a single sperm and inject it into the water component, also called the cytoplasm, of the egg. It is done after a woman has gone through an egg retrieval as part of an IVF cycle. Nationwide, ICSI is performed in 76% of all IVF cycles.

Why Is ICSI Done?

There are many reasons why your doctor may suggest ICSI for your IVF cycle. The most common reason is male factor infertility. This procedure can help overcome male factor infertility because it aides the sperm in fertilizing the egg.

Women whose partners have an abnormal semen analysis may be candidates for ICSI. One example of couples whom ICSI can help is those with high numbers of abnormally shaped sperm. Sometimes it is recommended if a couple has previously gone through an IVF cycle and had no fertilization or low fertilization of eggs. This procedure can also be used to fertilize an egg that has been frozen and then thawed.

How Is ICSI Done?

When an egg is retrieved from a woman’s ovary it is surrounded by a nest-like circle of cells called cumulus cells. These cells are removed from the egg by the embryologist in a process called “stripping” so that the egg can then be injected with a sperm. This is not done right away but when the egg has rested for a few hours after the egg retrieval.

Once the egg is stripped of the cells, the embryologist can tell if the egg is mature. It is normal to have a mixture of mature and immature eggs at the time of egg retrieval. Mature eggs (called MII, or metaphase 2 eggs) are the best candidates for ICSI. The embryologist then looks at all of the sperm under a microscope and selects one that has a normal shape and is moving well. This is the sperm that is picked up and injected into cytoplasm of the egg.

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How Do We Know if ICSI worked?

As with standard IVF, after the procedure is performed, the embryologist leaves the injected egg in an incubator overnight. The next morning, the embryologist does a fertilization check. A normally fertilized egg has a characteristic appearance. If there are two overlapping circles in the middle of the egg, the embryologist knows that the egg was fertilized. Those two circles, called pronuclei, come from the nuclei of the egg and the sperm, and indicate that the genetic material from both is combining to form a new entity, now called the embryo.

Egg fertilization rates after ICSI range from 50-70%. Not all eggs fertilize even though the sperm is injected into the egg; injecting the sperm into the egg promotes fertilization but, as in standard IVF, eggs subjected to ICSI must undergo a complex series of events that lead to successful fertilization. This technique has been used safely for over 30 years and has helped numerous couples around the world to become parents.

Original post August 31, 2015
Updated October 26, 2022