Intracytoplasmic sperm injection (ICSI) is a technique that has proven to be highly effective in the fertilization process, especially in cases of couples with male infertility issues.
In conventional in vitro fertilisation (IVF), sperm must penetrate the egg on their own, which can make the process difficult. However, with direct microinjection, the sperm is directly injected into the cytoplasm of the egg, thus facilitating the entire process.
The ICSI process begins with the collection of mature oocytes (fresh or vitrified, own or from a donor), while the semen sample is prepared to select the best sperm.
Under a specialised microscope, an embryologist injects a sperm directly into the cytoplasm of the egg. This step is crucial as it eliminates the need for the sperm to penetrate the egg on its own.
The fertilized eggs are cultured in a special medium and under optimal conditions for 5-6 days (recommended culture). After this period, embryos that reach the blastocyst stage can be frozen, biopsied, or transferred.
In vitro fertilisation (IVF) and ICSI technique are two fertilisation techniques used in assisted reproduction treatments, but they differ in their procedures. In IVF, the eggs and sperm are placed together in a culture medium for natural fertilisation to occur. On the other hand, ICSI involves the direct injection of a single sperm into the egg, which can improve the chances of fertilisation in cases of severe male-factor infertility.
ICSI is especially useful in cases of previous fertilisation failure with conventional IVF or when there are significant sperm quality or quantity issues. Learn about the differences between artificial insemination and in vitro fertilisation.
Intracytoplasmic sperm injection (ICSI) in assisted reproduction treatments is mainly indicated:
In cases of male factor infertility, when the semen analysis shows alterations such as a low sperm count, reduced motility or significant abnormalities in sperm morphology.
When there have been fertilisation failures or lower-than-expected fertilisation rates in previous conventional IVF cycles, with the aim of reducing the risk of this occurring again.
When it is necessary to use sperm retrieved directly from the epididymis or testicle, as may be the case in certain types of azoospermia.
When using previously vitrified eggs, as ICSI is the fertilisation technique commonly used after they have been thawed.
ICSI may also be considered in certain specific clinical situations, depending on the characteristics of the gametes, the patient’s reproductive history and the planned treatment. The choice between conventional IVF and ICSI should be made on an individual basis by the medical and embryology team.
Although this procedure allows a sperm cell to be injected directly into the egg, it does not guarantee that fertilisation will occur. The outcome also depends on the quality and maturity of the egg and sperm, as well as other biological factors involved in the process.
Following microinjection, the egg must successfully complete a series of cellular processes for fertilisation to occur and embryo development to begin. For this reason, even when the technique is performed correctly, some oocytes may not fertilise or may not continue to develop as expected. Fertilisation rates can vary depending on the individual characteristics of each case, so the embryology team assesses the development of the oocytes after ICSI on an individual basis.
ICSI is performed on the mature eggs retrieved during egg collection, as not all oocytes retrieved are necessarily suitable for microinjection. The number of eggs that are ultimately fertilised depends mainly on their maturity and quality, as well as the characteristics of the sperm and other biological factors specific to each case.
For this reason, not all eggs undergoing ICSI will necessarily fertilise successfully. After microinjection, the embryology team checks which eggs have fertilised normally and monitors their progress over the following days to assess embryo development.
ICSI can be performed using previously frozen sperm that is subsequently thawed. This option allows sperm samples to be stored for use in assisted reproduction treatment when required.
ICSI is a widely used technique and is generally considered safe. As with any assisted reproduction procedure, there may be certain considerations, usually related to the individual characteristics of the patients or the underlying cause of infertility. The medical team will assess each case individually before recommending the technique.