In natural conception, a sperm needs to find its way into the egg. To accomplish this, it has to reach the site of fertilisation, bind to the egg, tunnel through the shell and fuse with the egg membrane.

However, in some cases, the sperm may be unable to swim or penetrate the outer layer of the egg. Thus, intracytoplasmic sperm injection (ICSI), a technique which is done alongside IVF treatment, is crucial for fertilisation.

What is ICSI?

ICSI is a technique to inject a single sperm into an egg. The eggs are retrieved from a woman who undergoes fertility services such as in-vitro fertilisation (IVF). Healthy sperm is then selected and immobilised before being delivered into the egg’s cytoplasm.

ICSI treatment is most useful for couples with severe male factor infertility as it bypasses the initial steps of sperm-egg interaction

Not all eggs retrieved are suitable for ICSI. As shown from the diagram above, eggs go through several stages of maturity. Germinal vesicle-containing egg is the most immature stage, followed by metaphase-I (MI) and finally mature metaphase-II (MII). ICSI is only performed on mature MII eggs because only eggs at this stage are capable to fertilise.

The selection of sperm for ICSI is important for embryo development. Sperm health are assessed under the microscope for two parameters: motility and morphology. Forward–moving sperm (motility) with oval–shaped head, regular mid–piece and tail (morphology) are preferred for injection.

Fertilisation assessment is done the day after ICSI when the pronuclei (PN) are expected to appear. As illustrated above, the possible outcomes after ICSI are normal fertilisation, abnormal fertilisation or no fertilisation.

• An egg which is normally fertilised has 2 pronuclei, where one pronucleus originates from the egg and the other from the sperm.
• If the egg contains 3PN or more, or having just 1PN, this means abnormal fertilisation has taken place.
• If the egg does not show any PN, the egg has failed to fertilise.
• Sometimes, the egg does not survive the ICSI procedure and degenerate instead.

Intracytoplasmic sperm injection (ICSI) has become an important component of IVF treatment cycles. Find out more about the ICSI procedure we perform here at Alpha IVF.